aluminum cylinder block

Replacing the Cast Iron Liners for Aluminum Engine

Cylinder Blocks: A Comparative Assessment of Potential

Candidates

by

John Lenny Jr.

An Engineering Project Submitted to the Graduate

Faculty of Rensselaer Polytechnic Institute

in Partial Fulfillment of the

Requirements for the degree of

MASTER OF ENGINEERING IN MECHANICAL ENGINEERING

Approved:

_________________________________________

Professor Sudha Bose, Project Adviser

Rensselaer Polytechnic Institute

Hartford, Connecticut

April 2011

ii

© Copyright 2011

by

John Lenny

All Rights Reserved

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CONTENTS

CONTENTS ..................................................................................................................... iii

LIST OF TABLES ............................................................................................................ vi

LIST OF FIGURES ......................................................................................................... vii

ACKNOWLEDGMENT ................................................................................................ viii

ABSTRACT ..................................................................................................................... ix

1. Introduction .................................................................................................................. 1

1.1 Modern Passenger Car Fuel Economy .............................................................. 1

1.2 Increased Government Regulations ................................................................... 2

1.3 Automakers Ability to Meet New Regulations .................................................... 2

1.3.1 Objective of this Project ......................................................................... 2

1.4 Limitations of Current Cylinder Block Design .................................................. 3

1.4.1 Cylinder Block Requirements ................................................................. 4

1.5 Alternative Cylinder Block Solutions ................................................................. 7

2. Background .................................................................................................................. 8

2.1 The Cylinder Block ............................................................................................. 8

2.1.1 Cylinder Block Manufacturing ............................................................... 9

3. Methodology .............................................................................................................. 10

3.1 Hypereutectic Aluminum Silicon Alloy Cylinder Blocks .................................. 11

3.1.1 System Description ............................................................................... 11

3.1.2 Past Research and Development .......................................................... 14

3.1.3 Benefits of Hypereutectic Al-Si Alloys ................................................. 16

3.1.4 Drawbacks of Hypereutectic Al-Si Alloys ............................................ 16

3.1.5 Conclusions .......................................................................................... 17

3.2 Fiber or Particle Reinforced Aluminum Alloys for Cylinder Blocks ............... 18

3.2.1 Background Information – Defining a Composite ............................... 18

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3.2.2 Component Description ....................................................................... 19


3.2.4 Benefits of Fiber or Particle Reinforced Al Alloys .............................. 23

3.2.5 Drawbacks of Fiber or Particle Reinforced Al Alloys ......................... 25

3.2.6 Conclusions .......................................................................................... 26

3.3 Thermal Spray Coating of Aluminum Cylinder Block Walls ........................... 27

3.3.1 Process Description ............................................................................. 27


3.3.3 Benefits of Thermal Spray Coating ...................................................... 31

3.3.4 Drawbacks of Thermal Spray Coating ................................................. 32

3.3.5 Conclusions .......................................................................................... 33

3.4 Electroplating Aluminum Cylinder Block Bore Surface .................................. 34

3.4.1 Process Description ............................................................................. 34


3.4.3 Benefits of Electrolytic Coating Process.............................................. 38

3.4.4 Drawbacks of Electrolytic Coating Process ........................................ 39

3.4.5 Conclusions .......................................................................................... 40

4. Comparative Analysis ................................................................................................ 41

4.1 Comparison Categories ................................................................................... 41

4.1.1 Previous Applications .......................................................................... 41

4.1.2 Wear Resistance ................................................................................... 42

4.1.3 Scuffing Resistance............................................................................... 42

4.1.4 Thermal Conductivity ........................................................................... 43

4.1.5 Friction between cylinder block and piston rings ................................ 43

4.1.6 Fuel Economy....................................................................................... 44

4.1.7 Engine Emissions ................................................................................. 45

4.1.8 Manufacturing Costs ............................................................................ 45

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4.1.9 Engine Performance............................................................................. 46

4.1.10 Mass Production Feasibility ................................................................ 46

5. Summary .................................................................................................................... 47

5.1 Results of Comparison ..................................................................................... 47

5.2 Future of Alternatives ...................................................................................... 49

6. References .................................................................................................................. 54

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LIST OF TABLES

Table 1: Alternatives for Replacing Cast Iron Cylinder Bore Liners ................................ 7

Table 2: Development of Hypereutectic Al-Si for Automotive Engine Blocks .............. 14

Table 3: Comparison of various types of bore designs [28] ............................................ 24

Table 4: Comparison of Thermal Spray Processes for Aluminum Cylinder Bores [43] . 28

Table 5: Results of Comparison ...................................................................................... 47

Table 6: Results of Comparison based on Future MPG Requirements ........................... 50

Table 7: Applications of the Candidate Alternatives for Cast Iron Liners ...................... 51

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LIST OF FIGURES

Figure 1: Inflation Adjusted Average Annual Gasoline Prices 1918-2009 [1] ................. 1

Figure 2: Sulfur Concentration in unleaded fuel [28] ........................................................ 5

Figure 3: Breakdown of friction loss for engine components [34] .................................... 5

Figure 4: General Motors Inline Four Cylinder Block [55] .............................................. 8

Figure 5: Aluminum-Silicon phase diagram [45] ............................................................ 11

Figure 6: Principle of Operation for Hypereutectic Al-Si Alloy Cylinder Block [42] .... 13

Figure 7: Hypereutectic Al-Si Cylinder Block Surface Exposure Step [42] ................... 13

Figure 8: Different Fiber Orientations in a Composite [49] ............................................ 18

Figure 9: Aluminum-matrix MMC filled with Al2O3 agglomerates [45] ........................ 19

Figure 10: Cast Aluminum/Graphite Metal Matrix Composite Cylinder Liner [23] ...... 21

Figure 11: 2ZZ-GE MMC Cylinder Block [28] .............................................................. 22

Figure 12: Scheme of Thermal Spray Coating Process [46] ........................................... 27

Figure 13: Ford Sigma PTWA Apparatus ....................................................................... 30

Figure 14: Nickel Silicon Carbide composite applied to a cylinder bore [36] ................ 34

Figure 15: Plasma Electrolytic Oxidation Process [48] ................................................... 35

Figure 16: SEM micrograph of a typical PEO coating on aluminum [53] ...................... 36

Figure 17: Comparison of surface frictional coefficients for NCCs and Cr [34] ............ 38

Figure 18: Relationship of Emissions and Fuel Economy as MPG Requirement Increases

.......................................................................................... Error! Bookmark not defined.

viii

ACKNOWLEDGMENT

I would like to thank my family for their support over the years while I pursued

my degree. I would also like to thank Professor Bose for his guidance and support

throughout the process.

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ABSTRACT

The United States federal government has mandated that all automobile

manufacturers increase their vehicle fleet miles per gallon average to 35.5 by 2016. This

will challenge automakers to find ways to decrease vehicle weight and frictional loss

between powertrain components. One approach to increasing an automobile’s fuel

economy by reducing vehicle weight and friction loss simultaneously is to remove the

cast iron cylinder block liners and replace them with a lighter more thermally efficient

material. However, cast iron liners are needed on aluminum cylinder blocks because

they possess the necessary tribological characteristics. The focus of this paper is to

research possible alternatives to using cast iron liners for aluminum cylinder blocks. The

information gathered will be used to perform a qualitative comparison among the

alternative methods to assess their validity.

1. Introduction

1.1 Modern Passenger Car Fuel Economy

Recently in the United States a major shift has occurred in the public’s

perception of the importance of automobile fuel efficiency. The production of oversized

four ton gas guzzling sport utility vehicles has ended and has been replaced with smaller

more efficient passenger cars are being produced in greater numbers. There are several

factors that attributed to the focus of automobile fuel efficiency in this country. The first

is our susceptibility to oil market manipulation and the price shock. As a result of this

gas prices rose steadily from 1998 to 2008 with the national average for a gallon of gas

reaching $4.00 in July of 2008, Figure 1.

Figure 1: Inflation Adjusted Average Annual Gasoline Prices 1918-2009 [1]

Gases prices dipped from their historic highs in 2008 but have been creeping up again in

later stages of 2010 and into 2011.

Another reason for increased fuel consumption awareness is the growing concern

of pollution generated by automobile emissions. Research showed that the carbon

dioxide (CO2) produced from burning gasoline and diesel fuel in automotive engines is

contributing to global climate change [2].

2

Coupling of those first two factors with the struggling US economy at the end of

decade the moved the notion of conserving fuel and reducing emissions to the forefront

for government intervention. As a result, in 2009 the government stepped in to provide

the necessary legal enforcement of the decrease in emissions and increase in average fuel

economy for passenger cars.

1.2 Increased Government Regulations

On May 19, 2009 President Barack Obama proposed a new national fuel economy

program which adopts uniform federal standards to regulate both fuel economy and

greenhouse gas emissions while preserving the legal authorities of DOT, EPA and

California [3]. The program covers 2012 model year cars to 2016 model year cars and

ultimately requires an average fuel economy standard of 35.5 miles per gallon (mpg) by

2016 a increase from the current 25 mpg average for all vehicles.

President Obama said the program would save 1.8 billion barrels of oil “over the

lifetime of the vehicles sold in the next five years”. The increased miles per gallon

should cut greenhouse emissions by more than 900 million tons, the equivalent to

shutting down 194 coal plants.

1.3 Automakers Ability to Meet New Regulations

This new legislation for increasing the minimum mpg average for an automaker’s

fleet changes the design requirements for the automobiles sold in the United States. The

two major approaches for increasing automobile fuel economy is to improve powertrain

efficiency and to reduce the rolling resistance. The best approach for improving

powertrain efficiency is to reduce friction loss and the best approach for reducing the

rolling resistance is to reduce vehicle weight.

1.3.1 Objective of this Project

One of the ways to aid in an automobile’s fuel economy by reducing vehicle

weight and reducing friction loss simultaneously is to remove the cast iron cylinder

block liners and replace them with a lighter, more thermally efficient material. The

objective of this paper is to research and compare the different alternatives for replacing

3

the cast iron liners that are typically used in today’s modern passenger cars in

conjunction with an aluminum engine block. The information collected from the

research will then be used to perform a qualitative comparative analysis to find out

which alternative is the best replacement candidate.

Changes in the design for mass production are not taken lightly because of the

associated cost. Replacing the iron liners used in conjunction with aluminum cylinder

blocks is no exception. That is to say until recently when the government required that

all automobile fleets to increase the average fuel economy, the idea of replacing the iron

liners previously identified as too expensive, could become a necessity.

1.4 Limitations of Current Cylinder Block Design

In the past automakers have moved from cast iron to aluminum cylinder blocks

for weight shedding purposes. Replacing cast iron with aluminum for engine cylinder

blocks has the potential for a sizable reduction in block weight, up to 45% for gasoline

engines [5]. The downside to using aluminum as the cylinder block material is that the

traditional aluminum alloys do not have the required tribological characteristics for

required for engine block material. Therefore switching to aluminum for cylinder blocks

has created the need for surface engineering technologies capable of overcoming these

tribological characteristic deficiencies. Historically, the solution was to sleeve the

cylinder bores with cast iron to meet the required surface characteristics. Cast iron liners

are low-cost, durable, and easy to manufacture, which are the key criteria for mass

produced automobiles. That solution was perfectly fine until the federal government

mandated that automakers raise their fleet mpg average. Now the automakers are

searching into new ways or resurrecting old solutions to increasing automobile fuel

economy.

Moving away from cast iron sleeves gives the automakers an opportunity to

solve some of the secondary issues with using cast iron sleeves on aluminum cylinder

block bores. While cast iron liners are a cost effective solution at the moment, they have

the inherent disadvantages in weight, size, thermal conductivity, differential thermal

expansion and recyclability compared to the potential alternative materials. The

different thermal expansion coefficients of gray cast iron and the aluminum cylinder

4

block material can cause deformation of the liner and also local heat transfer problems if

the liner disengages from the engine block [32]. Particularly the deformation of the liner

leads to an increased oil and fuel consumption and increasing emissions. The liner-

equipped engine is still unnecessarily large, still has differential expansion and reduced

heat dissipation issues, still needs a heavier and larger cooling system, etc.

1.4.1 Cylinder Block Requirements

Internal combustion engine cylinder blocks must satisfy a number of functional

requirements. Within the cylinder, the combustion process produces rapid and periodic

rises in temperature and pressure, shear loading, and impingement of hot gases. The

extreme pressure from the combustion process induces circumferential and longitudinal

tensile stresses. The functional requirements include lasting the entire life of the vehicle,

housing internal moving parts and fluids, ease of service and maintenance of internal

components, and withstand pressures created by the combustion process. Cylinder block

bore surface material must have high wear resistance and capable of withstanding high

pressures on the order of 100 to 200 bar [7] in engines with high peak firing pressures.

The porosity level of the material must be below 1% and the maximum pore size must

be below 500 microns [7] on the running surfaces.

In order for cylinder block to meet these functional requirements the engineering

materials used to manufacture the product must possess high strength, modulus of

elasticity, wear resistance, scuffing resistance, and corrosion resistance. The material of

the cylinder block must be of a sufficient hardness to resist the wearing of the piston as it

slides up and down on the cylinder wall.

Two of the most important material characteristics that are needed for the

cylinder block surface are wear and scuffing resistance. Wear is erosion or displacement

of material from its original position on a solid surface performed by the action of

another surface [57]. Scuffing is the phenomenon characterized by mass movement of

surface elements to form linear scratches and local welds on surfaces in relative motion

[56]. Wear and scuffing occurs on the cylinder bore surface when the lubrication

conditions deteriorate. It is known that wear on the cylinder bore surface is promoted

when acid adheres to the bore surface during engine warm up as a result of sulfur in the

5

fuel [53]. Figure 2 below is a graph showing the sulfur concentration in gasoline in

various parts of the world. Toyota used this information to help guide their cylinder

block material selection for use in a sports car application in the late 1990s.

Figure 2: Sulfur Concentration in unleaded fuel [28]

Another important requirement for cylinder block material is its coefficient of

friction. Friction between the cylinder block surface and the piston rings has a major

impact on the efficiency of an automobile’s powertrain. Friction accounts for a loss of

over 40% of the total vehicle power [43]. Over half of that power loss can be attributed

to the frictional loss between piston rings and cylinder bores as shown in Figure 3 below.

Therefore in order for the alternative to be a viable option for replacing cast iron liners

the more it can reduce the frictional loss between the cylinder liner and the piston ring

Figure 3: Breakdown of friction loss for engine components [34]

6

The aluminum alloys used for cylinder blocks demand strictly controlled

characteristics and mechanical properties to meet the functional requirements mentioned

above in order to perform as expected in modern automobiles. In summary the key

characteristics that a cylinder block material must possess are as follows:

Cylinder Block Material Characteristics

High strength Low density

High Modulus of Elasticity Low thermal expansion

High wear resistance Good machinability

High scuffing resistance Good castability

High corrosion resistance Good vibration dampening

High thermal conductivity

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1.5 Alternative Cylinder Block Solutions

The four most promising alternative approaches for improving the tribological

characteristics of aluminum cylinder bores include hypereutectic aluminum silicon alloy

cylinder blocks, fiber or particle reinforced aluminum matrix composite cylinder blocks

or liners, thermal spray coatings on the cylinder bore, or electrochemical deposited

coatings on the cylinder bore. Each one of these four alternative approaches is discussed

in detail in this project. The first two alternatives are different material types altogether

compared to the traditional hypoeutectic aluminum alloys used for cylinder blocks. The

second two alternatives propose to maintain the use of hypoeutectic aluminum alloys but

to coat the bore surface with a hard wear resistant material that will meet the design

requirements. Table 1 below contains a description of each alternative with the key

characteristics of each in bold.

Table 1: Alternatives for Replacing Cast Iron Cylinder Bore Liners

Current Design

1. Hypoeutectic aluminum alloy cylinder block with cast iron cylinder bore liners

Alternative Designs

1. Hypereutectic aluminum silicon alloy cylinder block

2. Fiber or particle reinforced aluminum matrix composite cylinder block or

cylinder bore liner only with hypoeutectic aluminum silicon alloy cylinder block

3. Hypoeutectic aluminum silicon alloy cylinder block with cylinder bores coated

with a material deposited with a thermal spray process

4. Hypoeutectic aluminum silicon alloy with cylinder bores coated with a material

deposited with electroplating process

8

2. Background

2.1 The Cylinder Block

The cylinder block is the portion of the engine between the cylinder head and the

oil pan and is the supporting structure for the entire engine. All the engine parts are

mounted on it or in it and holds the parts in alignment. Large diameter holes in the

block-castings form the cylinder bores required to guide the piston. The surface of these

bores is commonly referred to as the cylinder walls. The cylinders are provided with a

web or bulkhead to support the crankshaft and head attachments. The bulkhead is well

ribbed to support the applied loads giving the block structural rigidity and beam

stiffness. The cylinder block has separate passages for the flow of coolant and

lubricating oil.

Figure 4: General Motors Inline Four Cylinder Block [55]

The cylinder block is a complex part to cast because of the crankshaft/head bulkheads,

bulkhead support ribs and the cooling passages. There are several different

configurations for cylinder blocks. The two most widely used configurations are inline

and v-banked cylinder blocks. A third configuration called horizontal opposed cylinder

block is used more sparingly for production cars.

9

2.1.1 Cylinder Block Manufacturing

Most of the automotive cylinder engine blocks made out of aluminum alloys are

currently manufactured by casting the block body in silica sand molds using sand cores

and inserting a set of cast iron liner to form the cylinder-piston contact surfaces. [7].

Other processes for casting blocks have included gravity feed semi-permanent molds,

high pressure die casting, low pressure die casting, the lost foam process and the zircon

sand package molds [7]. The cast iron liners can be inserted into the aluminum cylinder

block by a “cast-in” or “pressed-in” process. Cast iron liners have been placed like cores

in the casting mold for inclusion in the blocks or inserted in the machined cylinder bores

[25].

Typically when current cylinder blocks are cast of aluminum alloy they are either

made with 319 or A356 where A356 with a T6 heat treatment is gaining more

widespread usage for the US automakers. The T6 process is a solution heat treatment

and aging treatment used to increase the tensile and yield strength of the aluminum alloy.

A356 alloy meets or exceeds all the requirements for the mechanical strength, ductility,

hardness, fatigue strength, pressure tightness, fluidity, and machinability. Both alloys

require either cylinder liners or surface treatment to the cylinder walls to provide

sufficient wear resistance during operation. Aluminum alloys that can be suitably cast

and machined to make cylinder blocks have lacked cylinder wall wear resistance in

service. Engine manufacturers in the past have selected castable and machineable

aluminum alloys and then modified the cylinder wall surface to obtain the necessary

wear resistance [25].

10

3. Methodology

This project will cover the four main alternatives for replacing cast iron liners for

aluminum cylinder blocks. Each alternative will be characterized with a complete

system description, summary of past development, applications, and the positives and

negatives of that given approach. Information on each alternative will be gathered using

online engineering databases and articles from relevant technical publications. This

information will serve as the basis for making a comparative analysis between the

alternatives.

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3.1 Hypereutectic Aluminum Silicon Alloy Cylinder Blocks

One of the earliest approaches to eliminating the need for lining the cylinder block

bore surface was to cast the block out of a hypereutectic aluminum silicon alloy rather

than a traditional hypoeutectic aluminum silicon alloy.

3.1.1 System Description

A hypereutectic aluminum-silicon (Al-Si) alloy differs from previously used

hypoeutectic Al-Si alloys in that it has a higher concentration of silicon. A hypereutectic

Al-Si alloy is over saturated with silicon. During the formation of the alloy silicon

particles dissolve in the molten aluminum and become inseparable. However, above the

saturation point, known as the eutectic point, silicon will not dissolve but rather

precipitate out in crystal form. Typically, this saturation point in aluminum occurs

approximately at a 12% silicon concentration, shown in Figure 5 below. Commercial

grade hypereutectic Al-Si alloys range from 12% to 20% or more in silicon

concentration. Beyond 20% silicon concentration the alloys hardness reaches a level

where it can no longer be machined using traditional machinery. Therefore in terms of

minimizing casting costs for producing cylinder blocks it is important that the material

be machinable using standard tooling.

Figure 5: Aluminum-Silicon phase diagram [45]

The additional silicon concentration gives the hypereutectic Al-Si alloy adequate

hardness for use as a cylinder block material. Silicon is the second hardest element

12

behind diamond. The primary silicon particles of a hypereutectic Al-Si alloy that

crystallize out of the mold while the casting cools, is what increases the materials wear

resistance to an acceptable level for a cylinder block surface application. In addition to

the silicon content, small amounts of other elements are likely to be included such as

copper, manganese, magnesium, phosphorus, nickel, titanium, and strontium. These

additional elements improve the casting properties of the hypereutectic Al-Si alloy. For

instance, adding copper increases the fluidity of the molten aluminum during the pouring

process which improves the quality of the casting. Adding magnesium increases the

strength of the alloy at elevated temperature without increasing ductility. When a

hypereutectic Al-Si alloy is chosen as the cylinder block material, the optimum micro

structure for the casting is to have uniformly distributed primary silicon crystals in an

eutectic Al-Si matrix. The uniformly distributed primary silicon particles are the key

material characteristic for the cylinder block surface. If there is a large section of the

casting without silicon particles, that area will quickly be worn away by the piston rings

and could cause premature engine failure.

The operating environment of the internal combustion engine’s cylinder block is

very demanding. The speed at which the piston and piston rings reciprocate on the

cylinder block bore surface requires the material to be extremely hard and wear resistant.

The principle of operation for a hypereutectic Al-Si alloy as the cylinder block material

is shown below in Figure 6. The piston ring rides on a combination of lubricant and the

primary silicon particles in the aluminum.

13

Figure 6: Principle of Operation for Hypereutectic Al-Si Alloy Cylinder Block [42]

To ensure the piston rings slide on the hard primary silicon particles of the alloy

and not the parent aluminum material, a chemical etching is applied to the cast piece to

create a surface where individual silicon particles protruded a small distance above the

parent aluminum material [42]. This process in cylinder preparation is called the

exposure step shown below in Figure 7. The silicon particles form the supporting

structure for the pistons and piston rings.

Figure 7: Hypereutectic Al-Si Cylinder Block Surface Exposure Step [42]

14

After the exposure step is accomplished, the manufacturing process for the hypereutectic

Al-Si alloy cylinder block is similar to the process followed with a hypoeutectic Al-Si

with cast iron liners.

3.1.2 Past Research and Development

An early application of hypereutectic Al-Si alloy as a cylinder block material was

Porsche engines in 1960’s. The first application of hypereutectic Al-Si alloy for the US

market came in 1971 when General Motors (GM) used Reynolds A390 aluminum alloy

for the cylinder block in the Chevy Vega. GM did not have great success with the A390

aluminum because of the difficulty of casting the alloy with a uniform dispersement of

primary silicon particles. Since then there has been several key advancements in the

design of hypereutectic aluminum-silicon alloys for cylinder blocks captured below in

Table 2.

Table 2: Development of Hypereutectic Al-Si for Automotive Engine Blocks

Document Description/Impact

US Patent 3,895,941

July 22, 1975

G. F. Bolling, et. al.

Teaches a method of preparing an improved hypereutectic al-si alloy

One mode comprises the addition of sintered aluminum powdered rods

containing Al2O3 particles, uniformly distributed throughout, to a

hypereutectic melt of aluminum [21]

US Patent 4,434,014

February 28, 1984

David M. Smith, et. al.

Teaches properties of a castable hypereutectic aluminum alloy

Teaches Mi, Fe, and Mn are interchangeable with each other

Titanium is added to improve castability

High cost due to high content of Nickel

US Patent 5,217,546

June 8, 1993

John A. Eady, et al.

Development of a hypereutectic Al-Si alloy that has primary Si

particles uniformly dispersed and free of segregation

The alloy however relies on titanium and a large amount of nickel

which makes it an expensive alloy for mass production purposes

US Patent 5,316,070

May 31, 1994

Kevin P. Rodgers, et.

al.

Teaches a process for controlled casting of a hypereutectic Al-Si

Controlled cooling of the mold in critical areas, to remove/prevent

excessive accumulation of heat energy and avoid the formation of

intense convection currents

The growth of the Al-Si eutectic is promoted and the resultant

microstructure is substantially free of primary Si.

WO 2008/053363

Salvador Valtierra-

Gallardo, et. al.

Discloses an Al-Si alloy composition that meets the manufacturing and

performance conditions for liner-less cylinder engine block casting

using low-cost casting processes such as silica-sand molds

Uses the addition of sintered aluminum powdered rods containing

aluminum oxide particles, uniformly distributed throughout to a

hypereutectic melt of aluminum-silicon

15

3.1.2.1 Current R&D and Applications

In today’s automobile market manufacturers using hypereutectic Al-Si alloys

include Mercedes, Audi, Porsche, BMW, Volvo, VW, Jaguar, and Honda. Alusil®,

Lokasil®, Silitec ®, DiASil, Mercosil, ALBOND®, are all trade names or trademarks

for hypereutectic Al-Si for cylinder bore wear surfaces. In each case the engines using

the hypereutectic material are typically low volume, larger engines with six or more

cylinders. One of the leading manufacturers of hypereutectic Al-Si cylinder blocks is

KS Aluminum-Technologie AG (KS ATAG), a Kolbenschmidt Pierburg AG company.

KS ATAG has been producing hypereutectic Al-Si alloys for the last ten years. The

successful formulations are low-pressure die cast cylinder blocks made from

hypereutectic alloy AlSi17Cu4Mg and Alusil® [24].

Alusil® is a hypereutectic Al-Si alloy. KS ATAG produces cylinder blocks out

of Alusil® with a low-pressure die cast process. The cylinder block’s primary silicon

particles are formed during solidification as small, hard grains, on the surface of the

cylinder bores [24]. The silicon surface is porous enough to hold oil, and is an excellent

bearing surface. Alusil® is used in the majority passenger automobiles with larger, eight

cylinders or more, engines in Europe. Currently Audi, Volkswagen, BMW and Porsche

all use Alusil® for one or more of their production car cylinder blocks. Development of

hypereutectic Al-Si for the US market could come from KS ATAG importing their

technology or selling the rights to use their proprietary materials.

Another manufacturer with recent success with a hypereutectic Al-Si alloy

cylinder block is Mercury Marine. Mercury Marine created a castable copper-free

hypereutectic Al-Si alloy, Mercosil, for internal combustion engine cylinder blocks.

Along with primary silicon particles dispersed in the parent aluminum matrix, Mercosil

has particles of a solid lubricant embedded in the cylinder wall to further enhance the

wear resistance of the material. Through testing Mercury Marine has shown that the

copper-free hypereutectic Al-Si alloy Mercosil is superior to A390 hypereutectic

aluminum alloy in that Mercosil yields a more uniform distribution of primary silicon

and makes sound castings easier to produce, particularly in a slow cooling rate process

such as lost foam [20].

16

3.1.3 Benefits of Hypereutectic Al-Si Alloys

The validity of replacing cast iron lined aluminum cylinder blocks with an all

aluminum cylinder block made from a hypereutectic Al-Si alloy is dependent upon the

benefits it provides. Hypereutectic Al-Si alloys have the necessary wear resistance for

the cylinder block bore surface with a thermal conductivity of nearly 400% higher than

that of cast iron [20]. This benefits the operational efficiency of the engine because it

allows the heat to transfer more evenly thru the aluminum making the block easier to

keep cool, reducing the cooling load and therefore reducing the engine cooling system.

Uniformly transferring the heat from the combustion process enables the manufacturers

to design for higher operating temperatures which increases engine power and reduces

emissions.

Hypereutectic Al-Si alloys have high cycle fatigue strength 50% higher than that

of hypoeutectic Al-Si alloys [20]. Hypereutectic Al alloys do not require heat treatment,

which may eliminate internal stresses that may cause fatigue failure [7]. The low

coefficient of thermal expansion, high hardness and good wear resistance of

hypereutectic aluminum silicon alloy makes it an excellent choice for a lightweight

cylinder block material.

Hypereutectic Al-Si alloys also provide several benefits over cast iron block or

aluminum blocks with cast in liners in terms of manufacturing processes. Improving the

casting yield and producing a near net shape using hypereutectic Al-Si increases its cost

competitiveness over a long period of time compared to the traditional material

combinations. Hypereutectic Al-Si alloys enable foundries to use die casting instead of

sand casting which reducing machining costs and produces better material properties.

The all aluminum engines blocks are also highly recyclable, which cheapens the raw

material and energy consumption.

3.1.4 Drawbacks of Hypereutectic Al-Si Alloys

There are certain material characteristics that are preventing hypereutectic Al-Si

alloys from wholly replacing cast iron liners. Principally the reason being that

hypereutectic Al-Si alloys are extremely difficult to cast with the proper material

characteristics for cylinder blocks. General Motors was one of the first automakers to

17

find this out in the 1970’s, the Reynolds A390 hypereutectic aluminum cylinder blocks

they used for the Chevy Vega proved difficult to repeat the physical characteristics for a

mass production run of engine block castings. The tribological characteristics of

hypereutectic Al-Si alloys are determined by the distribution of silicon particles in the

as-cast condition. During the casting process it is difficult to control the distribution of

the silicon particles.

Cost also plays a role in preventing hypereutectic Al-Si alloys from being used in

modern passenger cars. Traditionally hypereutectic aluminums have expensive alloying

elements such as magnesium and nickel. Additionally hypereutectic Al-Si alloys require

a chemical etching step after the material is casted to expose the primary silicon particles

so that the piston and piston rings slide on only the silicon particles.

3.1.5 Conclusions

Hypereutectic Al-Si alloys for cylinder blocks has become an increasingly

attractive alternative for solving the tribological deficiency of most commercialized

aluminum alloys mainly as a result of improving the casting processes. Right now the

European car market has proven that hypereutectic Al-Si alloys become a viable

alternative for premiere luxury vehicles that have larger engines. Once the alloy is

commercialized in the US it will drop the price of the raw material and increase the

attractiveness of hypereutectic Al-Si alloy cylinder blocks.

18

3.2 Fiber or Particle Reinforced Aluminum Alloys for Cylinder Blocks

A second option for replacing aluminum cylinder blocks with cast iron liners is

to use a metal matrix composite (MMC). The composite material can be used for either

the entire block or as a MMC liner in conjunction with a common aluminum alloy. The

metal matrix composite cylinder blocks and liners are often referred to as fiber or

particle reinforced cylinder blocks in the automotive industry. Fiber or particle

reinforced is a description of the physical composition of the composite reinforcements.

3.2.1 Background Information – Defining a Composite

A composite is a material in which two or more distinct, structurally

complementary substances combine to provide structural or functional properties not

present in the individual component. The constituents are formed together by physical

means and not by chemical bonding of alloys. A composite is made up of a matrix, and

one or more reinforcements. The matrix provides the overall structure of the composite;

it surrounds the fibers. In the fiber reinforced composites, the fibers are individual

filaments of material embedded in the matrix that increase the composite’s strength and

other sought after properties beyond that of the individual matrix material. The fibers

can take the form of whiskers, which are single crystals of material, continuous fibers,

which are essentially infinite in length, or discontinuous fibers, which are short in length

but generally more than 3mm long [45]. The fibers can also have several difference

orientations within the matrix, as shown below in Figure 8.

Figure 8: Different Fiber Orientations in a Composite [49]

19

The reinforcement fibers aren’t necessarily added strictly for strength purposes, but the

fibers can also be used to change physical properties such as toughness, wear resistance,

friction coefficient, or thermal conductivity. Composites have unique combinations of

material properties that traditional monolithic materials do not have.

3.2.2 Component Description

As mentioned previously the focus of this section is on a certain type of

composite, one with a metal as its matrix material. Specifically, the metal matrix

composite that will be discussed here will be an aluminum matrix composite. Figure 9

below is an example of an aluminum-matrix (light areas) MMC filled with Al2O3

agglomerates (dark areas).

Figure 9: Aluminum-matrix MMC filled with Al2O3 agglomerates [45]

Metal matrix composites consisting of either continuous or discontinuous fibers

in a metal result in a material with combinations of very high specific strength and

specific modulus. Therefore, a metal matrix composite can be engineered to be a

suitable alternative for the cylinder block material to meet the requirements that a

traditional aluminum alloy cannot. The reinforcement fibers can be a multitude of

different materials, the most common being silicon carbide, a ceramic. The

reinforcement particles such as alumina, and boron carbide improve the scuffing

resistance to above that of cast iron. Compared to conventional aluminum alloys,

aluminum metal-matrix composites are much stronger at elevated temperatures. This

20

material characteristic is required for the cylinder block application because of the

thermal stresses the combustion process induces on the block.

During manufacturing of the MMC cylinder block, the fiber placement and metal

infiltration are important design parameters that affect the quality of the casting.

Typically the MMCs are made by placing fiber preforms in a mold and squeeze casting

the molten aluminum through the preform. The use of pressure ensures the molten

aluminum completely infiltrates the sponge like fiber preforms. Other researchers have

used an investment casting process to create a sound MMC casting without the use of

high pressure [50]. These infiltration methods have proven beneficial in the promotion

of finer casting grain structure which produces MMC cylinder block castings with

superior material properties.


Several automobile manufacturers have been successful in creating metal matrix

composites for production level engine cylinder blocks. Toyota Motor Company was

successful in producing an all-aluminum cylinder block with a MMC liner local to the

cylinder bores. The MMC liner preform consisted of alumina-silica fibers and mullite

particles [28]. Mullite is a refractory that increases the mechanical strength and thermal

shock resistance of the composite. Toyota produced inline four cylinder engine blocks

using this material combination.

Honda motor company was another automobile manufacturer to have success in

producing an all-aluminum engine block with a MMC lined cylinder bore. Honda

manufactured the cylinder blocks by placing cores of carbon fiber in an alumina (Al2O3)

matrix in the casting mold and then poured the molten aluminum around the cores [27].

The MMC cores absorbed the molten aluminum forming the reinforced cylinder bore

surface. After the casting was formed, the inner diameter of the MMC liner is bored out,

so that there is a 0.5-mm thick layer of material remaining. This small thickness of the

reinforced material provides the required wear resistance for the cylinder block

application. Honda used this material in both an inline four cylinder block and a v-

banked six cylinder block.

21

A picture of a MMC liner much like the ones Toyota and Honda created is shown

in Figure 10. The sectioned view on the right shows the smoothness of the machined

surface that the piston rides up and down on. The picture on the left is a graphite

reinforced piston.

Figure 10: Cast Aluminum/Graphite Metal Matrix Composite Cylinder Liner [23]

This particular cylinder block liner is a composite reinforced with graphite particles. The

graphite particles were added prior to the casting process, in which the graphite was

stirred in with the molten aluminum alloy and then poured into the mold. The cost of

producing cast MMCs has decreased rapidly in recent years, especially with the use of

low cost particulate reinforcements such as graphite and silicon carbide [23]. Silicon

carbide and graphite reinforcement composites are commercially available for other

applications.

A company mentioned in the previous section of this project, KS ATAG, besides

developing a hypereutectic Al-Si cylinder block, produced an aluminum matrix

composite suitable for engine cylinder blocks. KS ATAG patented Lokasil® which is an

engineered metal matrix composite whose microstructure consists of an aluminum alloy

matrix with silicon as the reinforcement material. Lokasil® is used as the cylinder block

bore surface material. KS ATAG’s MMC lined cylinder block is manufactured much

like Honda’s cylinder block where a Lokasil® preform is placed in the casting mold and

then molten aluminum is poured into the mold around the preform. The Lokasil®

preform absorbs the molten aluminum and the finished product is a silicon reinforced

22

aluminum cylinder block. KS ATAG’s first generation Lokasil® preforms contained 5%

volume alumina and 15% volume silicon and their second generation Lokasil II®

preforms had only 25% volume silicon [29] with no alumina content.

3.2.3.1 Applications

Toyota used their all-aluminum cylinder block with a MMC cylinder bore for the

seventh generation Celica sports car sold in the US starting in 2000. Production of the

Toyota Celica ended in 2006 but the motor with the MMC lined cylinder block was sold

to Lotus which was used in the Lotus Elise starting in 2005 and is still in production.

The code name for the Toyota 1.8 liter inline four cylinder engine is 2ZZ-GE. Figure 11

is a picture of the 2ZZ-GE’s engine block with a section cut showing the MMC liners for

cylinder bore surface.

Figure 11: 2ZZ-GE MMC Cylinder Block [28]

Toyota wanted to use one of their pre-existing engines for the basic structure that

they then could modify to increase the engine power for the Celica sports car. To do so,

Toyota chose the 1ZZ-FE engine, a 1.8 liter inline four cylinder engine. To use the same

cylinder block geometry from the 1ZZ-FE engine, Toyota needed to engineer a new

solution for developing more power within the same overall dimensions. Using the

principles of internal combustion engine theory, Toyota sought out to increase the piston

bore diameter and decrease the piston stroke, which would increase the engines cycling

capacity but require the distance between cylinder centers to decrease. After extensive

testing Toyota found that a MMC lined cylinder block would allow them to decrease the

23

distance between cylinder bore diameters to 5.5mm for the 2ZZ-GE. Toyota used a

laminar-flow die-casting process with specific control of the process parameters to

achieve sound cylinder block castings.

Honda Motor Company produced two sports cars sold in the US with fiber

reinforced aluminum cylinder blocks, the NSX (1990-2005) sold under their Acura

brand and the Honda S2000 (2000-2009). The Acura NSX was powered by a v-

configuration 6 cylinder engine with fiber reinforced blocks from 1997 to the end of the

its production run in 2005. The Honda S2000 was sold with an inline 4 cylinder engine

with fiber reinforced aluminum cylinder walls for its entire production run. Both were

low volume sports cars that much like the Toyota Celica had compact engines with the

capacity to operate at extremely high revolutions per minute. At higher engine speeds

the cylinder block material must have a higher wear resistance than a standard engine

which the fiber reinforced composite material exhibits.

KS ATAG’s patented Lokasil® material was used in several Porsche engines

sold in US. Lokasil® as the contact surface of the cylinder block has been used in the

2.5 liter and 2.7 liter flat six engines for the Porsche Boxster beginning in 1996 with the

2.5 liter block. Lokasil® has also been used in the 3.4 liter, 3.6 liter and 3.8 liter flat six

engines for the Porsche 911 Carrera beginning in 1997 with the 3.4 liter block. The

Lokasil® lined cylinder blocks were cast using a technique similar to Honda’s MMC

lined cylinder blocks. The process required inserting a preform of the reinforcement

material into the casting mold and allowing the molten aluminum to penetrate the

preform creating the hardened reinforced cylinder bore surface.

3.2.4 Benefits of Fiber or Particle Reinforced Al Alloys

There are several benefits an MMC cylinder block has over the traditional cast

iron lined aluminum cylinder block. MMCs are lighter than cast iron and are more

thermally conductive. This enables manufactures to keep engine displacement down

reducing component costs. Research and development testing by Toyota concluded that

in order to achieve a bore to bore distance of 5.5mm, MMC had the best properties in

terms of (a) between-the-bores rigidity, (b) between-the-bores strength, and (c) head

gasket surface sealing capability compared to hypereutectic Al-Si alloys, thermal spray

24

coatings, and electroplating coatings. The summary of Toyota’s assessment is shown in

Table 3.

Table 3: Comparison of various types of bore designs [28]

With a MMC cylinder block, it is easier to make high performance engine by

increasing the bore diameter without changing the bore stroke. For instance, Toyota

with their 1.8 liter four cylinder 2ZZ-GE engine, was able to produce 26.17% more

horsepower and 4.65% more torque with the same 1.8 liters of displacement as the 1ZZ-

FE that uses cast iron liners [28]. In the case of cast iron liner designs, the maximum

temperature between the bores would exceed the allowable limit. Focusing on high-

temperature strength of the sealing area between the bores, Toyota concluded that the

MMC bore design has an advantage for shorter bore-to-bore distances considering all

aluminum block designs [28]. The MMC bore material has a higher young’s modulus

[Fig. 4, 28], higher tensile strength at elevated temperature [Fig. 5, 28], and higher

compressive strength [Fig. 6, 28] than a hypoeutectic aluminum alloy with similar

mechanical properties as A380.

Lokasil® the MMC, patented by KS-ATAG, provides several advantages over

the traditional approach including weight reduction, a compact design with a minimal

block web width and low thermal deformation. These material properties enable

Lokasil® lined blocks to reduce bore distortion, lower oil consumption, reduced

emissions, and low wear of the engine and its components [22]. According to KS-

ATAG Lokasil® is cheaper than Alusil®, the hypereutectic Al-Si alloy mentioned

earlier, and is easier to process [22]. Basically KS ATAG was able to produce Lokasil®

liners with the proper surface finish without having to chemically etch the surface which

saves time and money.

25

Improved casting techniques by some foundries have provided opportunity for

MMC cylinder blocks to be cast with near net shape geometry in a simple, cost effective

manner. These improvements to how foundries produce MMC cylinder blocks increase

the production rates which is critical for the automotive industry. The casting techniques

include the ability to stringently control the distribution of the constituents, the

reinforcement wetting, and the solidification conditions of the cast MMC [23].

MMC with silicon carbide reinforcements have been developed with good

scuffing resistance and reinforcement distribution. MMC with graphite reinforcements

were also developed with scuffing resistance attributed to the graphite flakes acting as a

solid lubricant during testing.

3.2.5 Drawbacks of Fiber or Particle Reinforced Al Alloys

There are certain material characteristics that are preventing metal matrix

composites from wholly replacing cast iron liners. Engine failure can occur if the MMC

reinforcement particles are not evenly distributed throughout the cylinder bore surface;

the piston ring material can wear away the softer aluminum matrix in the absence of the

reinforcement particles. Once the cylinder bore is worn out, compression is lost and

engine failure will occur. The reinforcement distribution needs to be such that an oil

film can be maintained during operation. Engine durability tests have shown that too

much contact with piston ring material in absence of an oil film will lead to premature

wear and scuffing. After repeated contacts, some durability tests have shown that the

reinforcement material can be broken up if there is too much point contact with the

piston rings.

Problems can also occur if the reinforcement material in the aluminum matrix is

not set properly or is the wrong material type. If the reinforcement material is too hard

the reinforcement can prematurely wear out the ring which is equally as bad as a worn

cylinder bore, because worn rings decrease combustion efficiency and increase fuel and

oil consumption.

The downside to using the MMC block is the complicated and expensive casting

process to get acceptable product. Toyota went through this arduous process with the

2ZZ-GE engine. After much development they were eventually able to obtain castings

26

with near zero defect level in and around the bore areas. Toyota used a laminar-flow

die-casting process with specific control of mold temperature, squeeze pin and gas

discharge [28]. Issues with the casting process included metal infiltration around the

reinforcement fibers, reinforcement distribution, and post-casting machining.

3.2.6 Conclusions

To date the limited production applications of automobiles with fiber reinforced

composite cylinder blocks have been successful in the US market. When the Honda

S2000 sports car debuted in 1999 with a two liter four cylinder engine producing 240

horsepower, it became the most powerful naturally aspirated two liter four cylinder

engine in the world. One of the components that made it possible for Honda to

manufacturer an engine capable of safely producing power at 9,000 RPMs was the fiber

reinforced cylinder block. Going forward, the future implementation of MMC cylinder

blocks on a mass scale is dependent upon the ability of automakers to economically

produce the desired reinforcement distribution by infiltration, the improvement of fiber

matrix bonding, and the development of cost effective material combinations.

27

3.3 Thermal Spray Coating of Aluminum Cylinder Block Walls

A third alternative for replacing the cast iron liners for aluminum alloy cylinder

blocks is to coat the cast aluminum block cylinder bores with a thermal spray of wear

resistant, ceramic or composite material. The sprayed molten metal hardens to form a

suitable wear resistant surface for the aluminum cylinder block.

3.3.1 Process Description

Thermal spraying is the process of melting or heat softening of a material,

fragmenting and propelling the softened material in particulate form against a substrate,

in this case a cylinder block bore. The particles are propelled by a jet of process gases.

The particles accelerate as a confined stream towards the substrate. The heated particles

strike the surface, flatten, quenched, and get bonded to the aluminum. The coating

material is heated by means of an electric arc or combustion gases. In the thermal spray

process, the coating material is fed as a powder, wire or rod. Bonding of the coating to

the casting surface occurs principally by mechanical adhesion and only partially by

metallurgical bonding [30]. Figure 12 is a diagram showing the constituents of a typical

thermal spray process. Coating quality is determined by its porosity, oxide content,

macro and micro-hardness, bond strength and surface roughness.

Figure 12: Scheme of Thermal Spray Coating Process [46]

There are three main types of thermal spray processes suitable for coating

cylinder blocks on a mass production scale. They are electric arc spray, plasma spray

28

and high velocity oxy-fuel spray (HVOF). Table 4 is a comparison of the three major

types of thermal spray processes for aluminum cylinder bore applications.

Table 4: Comparison of Thermal Spray Processes for Aluminum Cylinder Bores [43]

Arc spraying process utilizes two wire electrodes fed into the spray torch and brought

into contact with each other at the front of the spray nozzle. An electrical load is placed

on the wires, one charged positively, and the other negatively, causes the bare metal

electrode tips to melt when they contact one another. An atomization gas such as air or

nitrogen is fed through the center of the spray gun that strips away the melted electrode

metal and propels it at the substrate. The plasma spray process utilizes an electric arc to

disassociate and ionize the atomization gas, which can be argon, nitrogen, hydrogen, etc.

being fed through the center of the spray gun. After the gas passes through the arc its

atomic components recombine, generating plasma that produces a significant quantity of

heat. It is here in the plasma that the coating metal in powder form is introduced into the

flame and propelled at the substrate by the plasma gas and secondary gases. HVOF

utilizes a combination of process gases injected into a combustion chamber of a torch

and ignited to create a high velocity flame. The flame is released through an orifice in

the torch’s nozzle. It is here that the coating material is fed into the flame through

another orifice in the nozzle in powder form. When coating material enters the flame it

melts and is accelerated towards the substrate.

The process of applying a thermal spray coating to a cylinder block is a

multistep process. First, the as-cast cylinder surface is bored to a rough diameter.

Second, the surface is cleaned and fluxed. Next, typically a bonding metal is applied to

29

thermally activate the flux and affect a metallurgical bond with the aluminum surface.

Once the flux and bonding agents have been applied, an iron oxide coating using one of

the thermal spray processes can be deposited. After coating, the cylinder block bore is

inspected for defects. Then it is honed to a final size and finish.


There is a number of thermal spray processes used in various industries today.

However, thermal spray technology is relatively new to the automotive world, especially

for coating the surface of cylinder block bores. For an automotive engine block

application thermal spray requires special adaptation to the existing spray systems used

in other industries. Typically the diameters of cylinder bores in modern passenger car

engines are smaller than 100 millimeters. The spray gun head needs to be able to rotate

coaxially in the cylinder bore to avoid having to rotate the cylinder block relative to the

spray gun. The gun head with the plasma generator or the combustion chamber and the

nozzle are mounted at the bottom of a rotating spindle.

Ford Motor Company was one of the early pioneers in the automobile industry

implementing a thermal spray process for cylinder block coating. Ford’s patented plasma

transferred wire arc (PTWA) process, is similar to the traditional arc spray process but

instead of normal gas as the atomizing medium, plasma gas is used. An arc is created

between a tungsten cathode and the copper nozzle acting as the anode. DC power is sent

down the cathode and anode. The power is transferred from the arc to the steel wire

feedstock, which is negatively biased to provide a sufficient conducting path. The

plasma gas is fed through the center of the gun radial ports in the cathode assembly to

produce a vortex and to atomize the molten coating . A secondary high velocity gas with

carefully controlled oxygen content is introduced just past where the plasma stream

intersects the wire arc.

30

Figure 13: Ford Sigma PTWA Apparatus

Source: Ford Motor Company

The molten iron globules combine with the oxygen in the secondary air to form wustite

an oxide of iron. Wustite is 70% harder than the steel matrix on which it forms [14].

The presence of iron oxides, specifically Fe2O3, in the plasma spray coating has been

shown to significantly increase the wear resistance [14]. Figure 13 is a picture of Ford’s

PWTA apparatus applying a coating on the aluminum inline four cylinder block. The

spray head drops down into the cylinder bore and rotates to coat the entire circumference

of the bore.


Ford has used their PWTA process on two US market cars to date. They are the

2011 Ford Mustang Shelby GT500, and the 2009 Nissan GTR. Ford licensed their

process to Nissan for the GTR. Both are high performance sports car, the Mustang has a

5.4 liter eight cylinder engine producing 550 horsepower and the 2012 version of the

GTR has a 3.7 liter six cylinder engine twin turbocharged engine producing 530

horsepower. The coating reduces friction between the piston rings and the cylinder

bores allowing the engine to build rotational speed quicker so that the motors produce

more power. In the Mustang the plasma sprayed coating saves 8.5 pounds weight over

the previous generation which had a cast iron lined aluminum cylinder block [52]. Fuel

economy has also increased 5% over the old model.

31

3.3.3 Benefits of Thermal Spray Coating

Thermal spray coating on aluminum cylinder block bores is the newest of the

four alternatives for replacing cast iron liners. It possesses several key benefits that aid

in the prospect of implementing the technology on a mass production scale. As of today,

only the plasma spray process has been used to coat production vehicle cylinder blocks.

The high thermal energy density available within the plasma used for melting the

powder coupled with the ability to manufacture powder, and design plasma guns with

short spray distances for specific applications has rapidly promoted the use of plasma

spraying [51].

Advantages of plasma sprayed coatings for cylinder bores include the reduction

in the cylinder block bore-to-bore distance, reduction in the friction between the piston

rings and the liner surface, increase in fuel efficiency, and reduction in the oil

consumption. Additionally the wear resistance of the plasma sprayed coating is higher

than cast iron. Recent development in rotating plasma spray guns using plasma-

powder spray process offers a cost-effective versatile high throughput surface

engineering tool for cylinder bore applications [31].

To qualify the plasma spray process for production level vehicles Ford performed

both laboratory and real world testing. It conducted many dynamometer and endurance

testing in the laboratory. Plasma spray lined engines exhibited half the amount of wear

of iron linings in a 300 hour full power endurance test [17]. Ford also put together a

fleet of vehicles with the plasma sprayed cylinder blocks that were driven on various

North American roads in different climates cumulatively for over a million miles. After

testing, Ford’s PTWA process was considered a success with the test data to back it up.

Results from Ford’s testing showed that friction was greatly reduced, on average 6.8%

below the values characteristic of traditional cast iron liners and 14.1% below cast-iron

engines [16]. At large, PTWA coated engines had increased miles per gallon of

gasoline, reduced wear, weight, and cost compared to their cast-iron counterparts [52].

In 2009, the engineers who perfected the PTWA deposition technique received the

National Inventor of the Year Award. The Intellectual Property Owners Education

Foundation cited the energy savings and positive environmental impact of the process.

32

3.3.4 Drawbacks of Thermal Spray Coating

The majority of the issues regarding thermal sprayed coatings for cylinder blocks

deal specifically with process types and not thermal spray in general. The most basic of

the drawbacks of the thermal spray coatings is the weakness of the bond between the

coated material and the aluminum. If the coating is not applied properly, over time de-

lamination can occur, stripping away the coating and exposing the soft aluminum block

material. Once that happens, premature wearing occurs and eventually the engine will

lose compression resulting in engine failure.

Additionally an issue with thermal spray processes pertains to any high velocity

spray coating. The coated material deposited on the substrate has a splatter morphology

from the high velocity impact of spherical particles striking the surface. Inconsistency in

coating properties occurs when the particles splatter against the substrate generating

pores in the coating. This can lead to cracking of the coating. Splatter morphology is

more of a concern with HVOF thermal spray because it utilizes high speeds to atomize

the coating material and with the short spray distances inside the cylinder bore splatter

morphology is more prevalent. In addition, during the application of the HVOF thermal

spray overheating of the aluminum cylinder block can occur because the particles are

still extremely hot when they bond with the substrate. Overheating can damage the

block by distorting it and possibly even changing the microstructure of the aluminum.

Another concern with thermal spray coatings is the initial capital investment of

the spray equipment. In order to coat cylinder blocks, existing production lines in the

plant will need to be either modified or new ones created to allow for the cylinder blocks

to be prepped and coated with a thermal spray process. The automaker would then be

relying on volume and reduction in cost per unit to ensure a timely buyback period.

33

3.3.5 Conclusions

Even though there is only a handful of production vehicles with cylinder blocks

that have been coated with a thermal spray process to date, plasma spray coating has

emerged as a promising alternative to cast iron liners. The process has already proven

itself worthy through extensive testing and market adoption. The coating material itself

is rather inexpensive. Therefore most of the burden of implementing the process for the

automaker is upfront equipment and logistic costs. Due to the high deposition efficiency

(over 80%) and high feed rates, the entire process can be completed in under 60 seconds

making it appealing on a mass market production level.

34

3.4 Electroplating Aluminum Cylinder Block Bore Surface

The fourth possible alternative to the replacement of cast iron liners for aluminum

engine blocks is to electroplate the cylinder bore walls with high hardness, wear resistant

materials. The electroplating processes used commercially or in the research and

development stage are nickel ceramic composite (NCC) coatings, and plasma

electrolytic oxidation (PEO) coatings. PEO coatings are also known as micro-arc

oxidation (MAO) coatings.

3.4.1 Process Description

Electroplating is a process where electrically charged metal ions in solution are

moved by an electric field to coat an electrode. The plating process uses electrical

current to reduce cations of a desired material from a solution and coat a conductive

object, in this case a cylinder block, with a thin layer of material [47]. Thus, the

deposition is the process of coating thin layer of one metal on top of a different metal to

modify its surface properties. One type of electroplating which is applied using the

aforementioned process for cylinder bore surface modification is NCC plating, also

referred to as NCC coating. NCC is a plating with nickel as the base material containing

particles of silicon carbide dispersed throughout, shown in Figure 14. The substrate in

this case is aluminum.

Figure 14: Nickel Silicon Carbide composite applied to a cylinder bore [36]

35

During the electroplating process the cylinder block is immersed in a bath of electrolyte

which typically consists of a salt or alkali solution such as potassium hydroxide (KOH).

The second type of electrolytic process used for coating cylinder block bore

surfaces is plasma electrolytic oxidation (PEO), also known as micro-arc oxidation

(MAO). Potentials of over 200 volts are applied between the two electrodes [37]. The

volts can be supplied as a continuous or pulsed direct current or pulsed alternating

current. Figure 15 is a diagram of the components of a typical PEO process.

Figure 15: Plasma Electrolytic Oxidation Process [48]

Plasma electrolytic oxidation is similar to conventional anodizing in that an appropriate

electrical potential is applied to aluminum to increase the thickness of the oxide layer on

the surface of the aluminum. Pure aluminum naturally forms a tough, wear resistant

oxide layer when first subjected to ambient air. It provides moderate protection against

corrosion. This oxide layer is common alumina and has a chemical formula Al2O3. In

conventional anodizing, this layer of oxide is grown on the surface of the aluminum by

applying an electrical potential while the part is immersed in an acidic electrolyte [37].

In plasma electrolytic oxidation, higher potentials are applied compared to

conventional anodizing. In the PEO of aluminum at least 200 volts must be applied.

This locally exceeds the dielectric breakdown potential of the growing oxide film, and

discharges occur. These discharges result in localized plasma reactors, with conditions

of high temperature and pressure which modify the growing oxide. Processes include

melting, melt-flow, re-solidification, sintering and densification of the growing oxide.

One of the most significant effects is that the oxide is partially converted from

36

amorphous alumina into crystalline forms such as corundum ( -Al2O3) which is much

harder [38]. Figure 16 is a scanning electron micrograph (SEM) of the splatter

morphology of a PEO coating on an aluminum substrate.

Figure 16: SEM micrograph of a typical PEO coating on aluminum [53]

Alternative NCC coatings include boron nitride (BN) for its self-lubricating

properties and silicon nitride (Si3N4) for its combination of wear resistance and self-

lubrication [34]. Self-lubricating properties afforded by the use of BN and Si3N4 also

offer greater flexibility in selection of mating materials while increasing the potential to

tighten tolerances between mating components [34].


Mahle developed a hard nickel based coating for the apex seals for the Wankel

motor in the early 1960s. Engineers at Mahle realized early that the nickel based coating

could also be applied to conventional engine cylinders, cylinder liners and sleeves to

reduce wear and improve lubricity [36]. The coating was named Nikasil®. It became a

registered trademark of the Mahle Company in 1967.

Nikasil® is an electrodeposited oleophilic nickel matrix silicon carbide coating

used on production engine cylinder bores. Nickel adheres to the parent bore material

and supports the silicon carbide particles that provide the necessary wear resistance and

hardness that is required for the cylinder block application. Silicon carbide is a very

hard abrasive material with a hardness second only to diamond [35]. The oleophilic

37

feature of Nikasil® gives it a natural tendency to absorb oil, which in turn helps the oil

retention of the coating increasing the life of the coating [36].

The process for depositing the oxide coating on aluminum anode under an arc

discharge condition was first reported by Markov and co-workers in the 1970s [39].

Many other researchers worked with the plasma electrolytic oxidation process

throughout the 1980s as well. It wasn’t until the research contributions by Yerokhin et

al. of Tula State University in the 1990s that the PEO process gained worldwide

recognition as an eco-friendly technology for depositing the tribologically superior

ceramic coatings on aluminum and its alloys [39]. A commercialized version of the

PEO process that Yerokhin et al. started is called Keronite. This process was developed

by a company in the UK working with the Russian originators. The Keronite process

creates a fused ceramic layer on the surface of the aluminum that is self-regulating, and

has a uniform thickness which includes the edges of the component.


Mahle initially developed Nikasil® to coat the rotary engine apex seals when the

Wankel motor was gaining popularity in the automotive industry in the late 1960s and

early 1970s. BMW, Porsche, Ferrari and Jaguar were some of the automakers to use

Nikasil® on production engines. During the 1990’s, in Europe, BMW coated several

production vehicle cylinder blocks with Nikasil® including two generations of 3 series

and 5 series, and one generation of both the 7 series and the Z3. Unfortunately because

of the high sulfur content in the gasoline sold in the US, BMW could not use Nikasil® in

US market vehicles. The low quality high sulfur gasoline caused some Nikasil® coated

cylinders to break down over time, causing costly engine failures. Another nickel based

coating, NiCom® was developed by US Chrome Corporation in the early 1990’s with

improved material characteristics. Porsche has maintained the use of Nikasil® in their

high performance variants of their 911 model.

Overall nickel ceramic coatings have been successful in high performance low

volume automotive engines due to their superior performance and lower deposition rate,

hence better control, compared to those of thermal spray technologies [43]. Before

38

NASCAR switched to Compacted Graphics Iron cylinder blocks, NCC was used to coat

the cylinder blocks for its lubricity and wear characteristics.

3.4.3 Benefits of Electrolytic Coating Process

There are numerous benefits that the different electrolytic coating processes have

over the traditional approach of lining aluminum cylinder blocks with cast iron sleeves.

The two main processes, NCC and PEO/MAO coatings, have properties that are

characterized by high hardness, high corrosion resistance, high temperature wear and

scuff resistance and low friction coefficients [34].

For the application of coating cylinder block bore surfaces in addition to high

hardness and corrosion resistance, the most effective property of NCC coating is its low

frictional coefficient. NCC is capable of contributing significantly to the reduction of

friction loss between sliding components. The friction coefficient of NCC coatings fall

in the 0.08-0.12 range, even under non-lubricated conditions [34]. Figure 17 compares

the frictional coefficients of several different electroplating materials. Hard chrome was

the original plating material for cylinder blocks but as the chart shows, the newer, more

advanced plating materials, have much lower frictional coefficients.

Figure 17: Comparison of surface frictional coefficients for NCCs and Cr [34]

When a NCC coating is applied properly, it will easily last the entire life of the

automobile. On a street-driven production vehicle, the coating can last upwards of

39

several hundred thousand miles because the coating wears very slowly compared to cast

iron, anywhere from 3 to 10 times better based on the application [36]. Depending upon

the alloy used and thickness of the coating applied on aluminum the hardness of

Keronite, a coating applied using the PEO/MAO technique, can reach 2,000 on the

Vickers Hardness scale, at least three times harder than hard anodizing [40]. In addition

to its high hardness, Keronite has a much stronger bond with the substrate material than

coatings applied with a plasma spray process.

When Nikasil® is used to coat the cylinder block bore surface this allows the

engine designers to reduce the distances between cylinder bore diameters with tighter

tolerances. It creates the opportunity for manufacturers to increase engine displacement

without increasing the overall size of the cylinder block.

3.4.4 Drawbacks of Electrolytic Coating Process

Unfortunately the electrolytic coating processes suffered through a very public

display of failure in the US in the 1990’s. The problem occurred specifically with

Nikasil®. BMW used Nikasil® to line the cylinders of several of their production

engines in the nineties. The problem arose from the fact that gasoline sold in the US has

a high concentration of sulfur as compared to Europe where the gasoline is basically

sulfur free. The sulfur broke down the nickel based coating causing “leak down” which

would result in a rough idle and eventually total engine failure. During engine testing

BMW used only sulfur-free gasoline so they had no idea that the problem was going to

occur before the cars made their way to the market.

Another drawback of electro-deposition processes is that the process is complex

and costly. Applying the coating to selective areas of the cylinder block requires either

a more complicated fixture that can apply localized deposition or extensive and elaborate

masking. The raw materials, specifically nickel, of the electrodeposited coatings are

more expensive relative to cast iron which hinders their ability to be used on mass

production automobiles. Another part of the manufacturing process adds to the overall

cost is the special machining tools needed to hone the coating to its final thickness. The

coatings have a hardness that requires special diamond tipped cutting tools for the

honing process.

40

3.4.5 Conclusions

The key aspect of the potential widespread use of electrolytic coatings for

aluminum cylinder blocks for the US market is what happens to the sulfur content in

gasoline. Currently, Europe has all but eliminated sulfur from its gasoline, while the US

gasoline can still have up to 95 parts per million (ppm). In the spring of 2010, the US

Environmental Protection Agency (EPA) was instructed by the Obama Administration to

research the effect of sulfur levels in gasoline on greenhouse-gas emissions. To date, the

EPA hasn’t reached any conclusions or proposed any new rules for lower-sulfur

gasoline. If the EPA does impose new regulations in the future for sulfur free gasoline

in the US, then that would pave the way for electrolytic coatings to be considered for

widespread use.

41

4. Comparative Analysis

Up to this point in the project information that pertains to each alternative has been

discussed in great length. Using that information a comparative analysis of the

alternatives is as follows:

Category Rating System

5 = Excellent

4 = Above Average

3 = Average

2 = Below Average

1 = Poor

4.1 Comparison Categories

4.1.1 Previous Applications

Cast Iron = 5 Hypereutectic Al-Si = 2 Fiber Reinforced = 1 Thermal Spray = 1 Electroplating = 2

Citing previous applications of the alternatives gives a basis for the confidence that the

automotive industry has in the alternative method for replacing the cast iron liners used

with aluminum cylinder blocks. Until the recent development with the increased CAFÉ

mpg average, the majority of the production automobiles with aluminum engine blocks

have had cast iron cylinder liners. There are examples of larger passenger automobiles

with hypereutectic Al-Si alloys in Europe. Most of the production model vehicles use

Alusil®, an alloy patented by KS ATAG in Germany. On a comparative basis, there are

fewer production models with fiber reinforced cylinder blocks than hypereutectic Al-Si

cylinder blocks. Toyota and Honda have had success using fiber reinforced composite

materials on several US market sports cars. Thermal spray technologies are a newer

alternative. Only two US market automobiles have thermally sprayed cylinder bore

surfaces. Lastly, electroplating has had success in low volume sports cars for many

years. There were production models in the US that used Nikasil®, one type of

electroplating, in the 1980’s. However, there were problems with the performance

42

because of the sulfur content in US fuel. Sulfur would attack the plating and premature

engine failure would occur.

4.1.2 Wear Resistance


Resistance to wear from a sliding surface is one of the key characteristics that a cylinder

block material needs to exhibit. The harsh environment of an internal combustion

engine can easily damage softer materials. Several researchers have performed

extensive wear resistance testing of the alternatives for cast iron for cylinder block bore

material. The results show that cast iron’s wear resistance with its tendency to hold

lubricating oil because of its porous nature is excellent. Cast iron also showed an ability

to resist wear at elevated temperatures better than the alternatives. Both thermally

sprayed oxide coatings and electroplated nickel ceramic coatings demonstrated excellent

wear resistance. The problem being that the two coatings are so hard, they can damage

the piston and piston rings, more so with the thermally sprayed oxide coatings. The fiber

reinforced and hypereutectic Al-Si alloys performed well in testing with acceptable wear

resistance. The fiber reinforced composites and hypereutectic Al-Si don’t rate as highly

compared to the alternatives because their wear resistance is based on the dispersed

particles of the additive elements that give the alternative materials sufficient wear

resistance. If the dispersed particles are large enough and evenly mixed, wear can occur

where large areas of the softer parent aluminum material is prevalent.

4.1.3 Scuffing Resistance


A cylinder block material’s ability to resist scuffing is another important characteristic.

As discussed earlier, scuffing occurs right after the engine is turned on and the cylinder

block is still cold. The importance of scuffing has led several researchers to develop

scuffing resistance testing comparing the alternative materials to cast iron for cylinder

block bore surfaces. The scuffing resistance testing had similar results as the wear

resistance testing, which would be expected because both tests have similar setups and

43

rely on similar material behavior. Simply stated, the test involves a reciprocating load

that is cycled over the test material to emulate the action of the piston and piston rings on

the cylinder bore surface. Material/scuffing is observed and recorded. Cast iron again

demonstrated the best scuffing resistance followed by the nickel ceramic coating applied

by the electroplating process. The thermally sprayed oxide coating also performed well

in scuff resistant testing. Therefore, it could be summarized that the hypereutectic Al-Si

alloy, the fiber reinforced composite Al alloy, and the thermal sprayed oxide coating

demonstrated equal and sufficient scuffing resistance.

4.1.4 Thermal Conductivity


Thermal conductivity is the property of a material’s ability to conduct heat. The thermal

conductivity of the cylinder block material is important in controlling the operating

temperature of the internal combustion engine. The cylinder blocks ability to gain or

lose heat impacts the efficiency of the combustion process which in turn impacts the

engines fuel efficiency and emissions. The more thermally conductive the cylinder

block material is, the easier it is for the cooling system to maintain a constant

temperature through the material thickness. This eliminates the possibility of hot spots

in the cylinder block which over time can lead to cracking and failure of the block.

Aluminum is three times more thermally conductive than cast iron. The hypereutectic

Al-Si alloys and the fiber reinforced composite alloys have better thermal conductivity

than cast iron. The material used in the thermal spray process and the electrochemically

deposited material are not as thermally conductive as the two aluminum alloys are.

However, they are better than the cast irons. The coating thicknesses are much thinner

than the cast iron liners which allows for easier transfer of heat between materials.

4.1.5 Friction between cylinder block and piston rings


44

The friction between the cylinder block bore material and the piston rings is the single

biggest contributor to the loss of power in an internal combustion engine. Limiting this

friction goes a long way in increasing the fuel efficiency of an automobile outside of

reducing vehicle weight. The best alternative for reducing friction is the thermally

sprayed coating material. The coating is extremely hard and its ability to retain a layer

of oil for lubrication during operation is key for reducing the coefficient of friction. The

electrodeposited material with its high hardness is another good candidate material for

reducing friction. The two aluminum alloys, the hypereutectic Al-Si and the fiber

reinforced composite, exemplify satisfactory results during testing. Both material

performances are dependent upon the hardening particles dispersed in the parent

aluminum. The more evenly the particles are dispersed in the aluminum, the better the

material can provide a smooth sliding surface while maintaining the ability to retain oil

for lubricating purposes. Cast iron is the basis of the comparison and demonstrates

acceptable performance.

4.1.6 Fuel Economy


Fuel economy or fuel consumption is the measurement of how much fuel the

automobile’s internal combustion engine uses over a given distance. In the US the unit

of measure is mile per gallon. This category is important to validate the assessment of

replacing cast iron liner on aluminum cylinder blocks. Engine fuel economy will

become more important to automakers in the near future due to the increased

government CAFÉ standards. Researching the alternatives has led to the conclusion that

all four candidates will increase the fuel economy of a given engine by replacing the cast

iron liners. Typically the aluminum alloys and the coatings can increase the vehicle’s

fuel economy on average by 3 to 5%.

45

4.1.7 Engine Emissions


Engine emissions are the byproducts of the automobile engines combustion processes

that exit the tailpipe of an automobile and enter the atmosphere. The subject of

automobile emissions has become more important in recent times due to the increased

awareness of their impact to the planet’s ecosystem. The Government’s increasing the

CAFÉ standards solves multiple issues, it decreases our country’s dependency on

foreign oil, but also it decreases the amount of automobile emissions which has a

positive impact on the environment. The results here for this comparison are the same as

the fuel economy results. Each alternative holds a slight advantage over the previous

solution of lining the cylinder bores with a cast iron sleeve. This stems from the fact that

each alternative slightly increases the fuel efficiency of the engine which will decrease

the engine emissions by a small amount.

4.1.8 Manufacturing Costs


The alternative material’s production costs are those associated with the material

procurement, casting process, specialized tooling, coating process (where applicable)

and post-cast machining. The costs associated with using cast iron sleeves with

aluminum alloy cylinder blocks are considered baseline. To date, the cast iron liners are

the cheapest solution. Each one of the alternatives has associated costs that increase the

total production cost beyond the baseline costs. The perfect hypereutectic Al-Si alloy

for the cylinder block application has not been commercialized to date. This means that

if an automobile manufacturer wants to use a hypereutectic Al-Si for their cylinder

blocks, they must incur the development costs of producing a new hypereutectic Al-Si

alloy. Hypereutectic Al-Si alloys are difficult to cast with the right consistency of

primary silicon particles throughout the bore surface. Both hypereutectic Al-Si alloys

and fiber reinforced composite Al alloys require expensive post cast machining.

Thermal Spray coatings require additional equipment costs of procuring the machine that

sprays the coating. Electrochemical deposition coatings also require the procurement of

46

the apparatus that will apply the coating. The material used in electroplating is more

expensive than cast iron.

4.1.9 Engine Performance


Engine performance for purposes of this comparison relates to how each alternative

affects engine longevity, power production and maintenance. The two coating

alternatives, thermal spray and electroplating both exhibit excellent performance at

elevated temperatures allowing for automakers to design the engine to operate at a

higher compression ratio. That creates a hotter combustion process putting more stress

on the cylinder block and other engine components. The fiber reinforced metal matrix

composites also exhibit excellent performance at elevated temperatures. There are

several examples of fiber reinforced composites, plasma sprayed iron oxide, and nickel

ceramic carbide used in high performance applications. In terms of longevity and

maintenance, cast iron liners have proven to be a perfectly viable solution as a result of

being used consistently for many years.

4.1.10 Mass Production Feasibility


The alternative choices to using cast iron liners for aluminum cylinder blocks may be

feasible on a mass production scale. It’s an important parameter in this comparison.

Currently in the US, cast iron liners are used in the majority of the production vehicles

sold with aluminum cylinder blocks. Assuming that in the future the automakers need to

move away from cast iron liners because of the increased fuel economy standard, plasma

sprayed coatings have the greatest ease of being implemented on a mass production

scale. This is a result of thermal spray coatings having a combination of cheaper

material cost and short manufacturing time relative to the other alternatives.

Hypereutectic Al-Si alloys and fiber reinforced composites suffer from increased

material costs. Electrolytic process coatings take a considerable amount of time to

achieve the proper coating thickness in the bath.

47

5. Summary

5.1 Results of Comparison

The results of the comparison in this paper are based on a combination of research

data and engineering judgment. The objective of the project was to assess the validity of

selected alternatives replacing the cast iron liners that are used to fortify aluminum

cylinder blocks for passenger cars. Ten different parameters were used to compare the

validity of the alternatives against one another and against cast iron liners. The results of

the comparison are summarized below in Table 5.

Table 5: Results of Comparison

Current Design Score out

of 50*

Cast Iron Liners with Hypoeutectic Al-Si Cylinder Block 38

Alternative Design

Hypereutectic Al-Si Alloy Cylinder Block 33

Fiber Reinforced Aluminum Matrix Composite Cylinder Block 32

Thermal Spray Coating on Hypoeutectic Aluminum Bore Surface 37

Electrochemical Deposition Coating on Hypoeutectic Aluminum

Bore Surface 34

* Score is the sum of rankings assigned in the ten categories

The results show that cast iron liners based on the parameters of the comparison

is still the best option for today’s modern passenger car cylinder blocks. As it was cast

iron liners rated very well in terms of previous applications, cost, and mass production

possibility including being the current industry standard. The best alternative proved to

be thermally sprayed cylinder bore coatings. Thermal spray coatings rated well in

minimizing frictional losses between the cylinder surface and the piston rings and mass

production possibility. Electrochemically deposited coatings proved to be the second

best alternative in the comparison. Electrochemical deposition coatings are of high

quality and high wear and scuff resistance. But they suffer from production cost issues.

48

Nickel used in many of the electrochemically deposited coatings is more expensive than

cast iron. Also the post cast machining processes for an electroplating can be

expensive. Hypereutectic Al-Si alloy and fiber reinforced aluminum matrix composite

cylinder blocks came in right behind electrochemically deposited coatings in the

comparison with one point separating each one from another. Hypereutectic Al-Si alloy

cylinder blocks performed well in most categories but did not perform exceptionally

well to establish it ahead of the other alternatives. Fiber reinforced aluminum matrix

composite cylinder blocks or cylinder liners had very similar results as hypereutectic Al-

Si alloy cylinder blocks which is not surprising because the two approaches have similar

material characteristics. Table 7 summarizes the applications of each alternative to date.

49

5.2 Future of Alternatives

The United States federal government has proposed legislation that would require

automakers to have a vehicle fleet with an average mpg of 35.5 by 2016. The objective

of the legislation was to reduce our dependency on foreign oil and to reduce vehicle

emissions. The new legislation will force automobile manufacturers to make design

decisions on future vehicles based on how the design affects fuel economy performance.

As stated previously, the two major factors that impact automobile fuel economy are

vehicle weight and frictional losses. Therefore, it is up to the automobile manufacturers

to find ways to increase automobile fuel economy without drastically increasing the cost

of the vehicle in order to stay competitive in the market.

In the future the MPG requirement for passenger cars will reach a level where cost

is not the determining factor for the incorporation of certain designs because the increase

in fuel economy performance from the design is a necessity. One such design change

that in the future will be made based heavily on fuel economy performance is replacing

the cast iron liners used with aluminum engine blocks. Currently, the cast iron liners are

the best solution because cast iron is a cheap readily available material and meets the

requirements of a cylinder block bore surface material. In the future the cast iron liners

will be replaced because cast iron doesn’t have the capacity to increase vehicle fuel

economy and reduction of emissions that are inherent to the alternatives.

Another one of the determining factors that was used in the comparison that

wouldn’t have the same impact in the future is previous applications. Once the MPG

requirement reaches that level where the cast iron liners must be replaced, the

automobile manufacturers will no longer be able to decide on a path that they already

feel comfortable with and had success with in previous applications, the cast iron liners.

The manufacturers will need to spend the research and development resources and prove

to themselves that they can implement a new more fuel efficient solution to the

aluminum cylinder block bore material problem.

A third determining factor that was used in the comparison that wouldn’t have

the same impact in the future is mass production feasibility. Again, once the MPG

requirement reaches the level where the cast iron liners must be replace, the automakers

50

will need to spend the resources developing new manufacturing techniques that will get

them the required production rates that are necessary for passenger cars.

Once the manufacturing cost, previous applications, and mass production

feasibility categories are removed from the future MPG requirement comparison the best

solution is a thermally sprayed coating on the cylinder block bore surface. The results of

the comparison are summarized in Table 6 below.

Table 6: Results of Comparison based on Future MPG Requirements

Current Design Score out

of 35*

Cast Iron Liners with Hypoeutectic Al-Si Cylinder Block 23

Alternative Design

Hypereutectic Al-Si Alloy Cylinder Block 24

Fiber Reinforced Aluminum Matrix Composite Cylinder Block 25

Thermal Spray Coating on Hypoeutectic Aluminum Bore Surface 28

Electrochemical Deposition Coating on Hypoeutectic Aluminum

Bore Surface 27

* Score is the sum of rankings assigned in seven categories

The score above is the sum of the rankings from the remaining seven categories used in

the original comparison. The seven remaining categories are attributes that characterize

the performance of the alternative regardless of cost, previous applications, and mass

production feasibility. Therefore, in the future, as the MPG requirement continues to

increase, the best alternative to cast iron liners is to coat the aluminum cylinder bore

surface with a wear resistant material applied using a thermal spray process.

Table 7: Applications of the Candidate Alternatives for Cast Iron Liners

Candidate Alternative

Prior/Current Application Cylinder

bore

surface

properties

Opportunity

for mass

production Volume Cost

Hypereutectic Al-Si

alloy cylinder blocks

Alusil® Large engine (8 cylinders and more)

High Med Med High European passenger cars

Mercosil Outboard motors, small European cars High Med Med High

Cylinder bore

coatings applied

with a thermal spray

process

plasma transfer wire arc Ford Mustang Shelby GT500, Nissan

GTR Low Low Med High

High velocity oxy-fuel None to date n/a High High Low

Rotating air plasma spray None to date n/a Low High High

Fiber reinforced

aluminum matrix

composites

Silicon carbide fiber reinforced

aluminum matrix composite

Toyota Celica, Lotus Elise, Honda

Prelude and S2000, Acura NSX Low Med Med Low

Lokasil® Porsche Boxster, Porsche 911 Med Med Med Med

Cylinder bore

coatings applied

with an electrolytic

process

Nickel ceramic composite Numerous Porsche, BMW, Jaguar,

Ferrari models High High High Low

Plasma electrolytic oxidation None to date n/a Low High Med

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