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Processing Parameters Effect on Friction Stir Welded

Aluminum Matrix Composites Wear Behavior

Journal: Materials and Manufacturing Processes

Manuscript ID: LMMP-2012-0118.R3

Manuscript Type: Original Article

Date Submitted by the Author: n/a

Complete List of Authors: Hassan, Adel; Jordan University of Science and Technology, Industrial Engineering Department Almomani, Mohammed; Jordan University of Science and Technology, Industrial Engineering Department Qasim, Tarek; Jordan University of Science and Technology, Industrial Engineering Department

Ghaithan, Ahmed; Jordan University of Science and Technology, Industrial Engineering Department

Keywords: welding, wear, tribology, stir, silica, reinforcement, graphite, friction, composites, ceramics, aluminum

URL: http://mc.manuscriptcentral.com/lmmp Email: [email protected]

Materials and Manufacturing Processes

For Peer Review O

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Processing Parameters Effect on Friction Stir Welded Aluminum Matrix

Composites Wear Behavior

Adel Mahmood Hassana*, Mohammed Almomani

a, Tarek Qasim

a, Ahmed

Ghaithana,

a Department of Industrial Engineering, Jordan University of Science and Technology. P.O. Box 3030,

Irbid 22110, Jordan.

ABSTRACT

In the present work, the aluminum matrix composites reinforced with both SiC and

graphite particles are joined using a friction stir welding (FSW) process. The wear

characteristics of the welded joints were investigated at constant load of 50 N and a

rotational speed of 1000 rpm using a pin-on-disk wear testing apparatus. This study

focuses on the influences of the FSW processing parameters (tool geometry, rotational

speed, and welding speed) on the wear characteristics of the welded joint of the

considered hybrid aluminum matrix composite under dry sliding conditions. The

experimental results indicate that the wear resistance of the joint increases at high

welding speeds (> 45 mm/min) and/or low value of rotational speeds. Different tool pin

profiles (square, octagonal, and hexagonal) are developed to perform the welding

process, and the effects of the tool pin profile on the weldments were studied. It is found

that joints welded with square pin profile have better wear resistance compared to the

other pin profiles. The results demonstrate that the FSW processing parameters greatly

affect on the wear resistance of the welded joints due to various microstructural

modifications during welding that cause an improvement in the welded zone hardness

and wear properties.

Keywords:

Aluminum; Composite; Friction; Welding; Wear

*Corresponding author Tel: +962-2-7201000, Ext: 22571

E-mail address: [email protected]

1. INTRODUCTION

At present, there is a continuously increasing demand for high strength and light weight

materials in transport and aerospace industries. These materials are more energy efficient

in terms of reducing fuel consumption. Aluminum matrix composite (AMCs) is one of

the promising candidate materials which have a great potential in the applications where

a weight reduction is critical [1,2]. They have outstanding attractive properties, i.e.

inexpensive, low specific density, high strength, good mechanical and wear properties

[3,4].

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Both fibers and particles reinforcement can be used in the aluminum matrix of AMCs.

SiC, Al2O3, SiO2, BN, and graphite are examples of the reinforcement particulates that

used commonly in AMCs [5]. Even though, the great advantages of the AMCs, the

difficulties associated with joining them together or with different materials using the

conventional fusion welding techniques limit their use in the industrial applications [6].

Fortunately, a new solid state joining process named as friction stir welding (FSW),

succeed to overcome many welding difficulties associated with the conventional fusion

welding processes [7]. Nowadays, welding and joining of AMCs to themselves or other

materials become possible and the market share for metal matrix composites (MMCs)

increased extensively [8].

Many of the products and the components made from AMCs are moving and sliding

parts, i.e. brake drums, cylinder blocks and drive shafts [9]. Due to the fact that the

production of these components involves the use of various secondary operations, i.e.,

machining, joining, etc. Then, it is very important to fully establish the wear

characteristics of the weld joint of AMCs in order to build a solid understanding of their

behavior in service condition.

The studies on the dry sliding wear behavior of aluminum alloys illustrate that the metal

matrix composites reinforced with hard particles are more resistive to wear than the

corresponding monolithic alloy [9]. It was observed that the addition of SiC particulate

to the aluminum matrix makes it harder, stronger, and more resistive to wear. This

increase in the hardness will be at the expense of machinability. Therefore, graphite

particles are used to maintain the gain achieved by SiC addition and concurrently

improve machining as well [1]. These considerations were an encouragement to select the

considered hybrid aluminum matrix composite with the two reinforcements particulate

(SiC and graphite) in the present study. Therefore, the present work differs from most

other earlier studies that focused on AMCs reinforced by only one type of reinforcement

by ceramics particles.

Optimization of the effect of the FSW processing parameters on the weld joint

performance has been of the interest of many researchers [10]. C. Meran and O.E.

Canyurt observed that fine grain structure formed at higher welding speeds due to a lower

heat input to the welding zone. In contrast, coarser grains generated at lower welding

speeds as a result of the increased heat input [11]. Furthermore, several researchers

studied the influence of the welding tool design parameters on the strength of the weld

joint [12-15].

Few researchers studied the wear resistance of FSW weld zone for Al based MMCs [16].

Hence, the present investigation is an attempt to assess the effect of the FSW processing

parameters (tool profile, rotational speed, and welding speed) on the wear resistance of

the considered welded hybrid composite joints under dry sliding conditions.

2. EXPERIMENTAL PROCEDURE

Plates of aluminum matrix composite with chemical composition shown in table 1 (100

mm x 75 mm x 7.5 mm) were butt friction stir welded using a special fixture. This

fixture was fixed firmly on the table of a conventional milling machine. The machine

spindle equipped with a welding tool. The working parameters used for friction stir

welding are shown in Table 2. Samples from the nugget zone of the friction stir welded

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plates were cut in a length of 25 mm in the welding direction and 20 mm in the transverse

direction. All samples were grounded with emery paper 800, and 1200 grit size, and

washed with water and alcohol to get rid off any left contamination.

The effects of the FSW processing parameters (rotational speed, welding speed, and tool

pin profile) on the dry sliding wear rate of the welded zone of the considered hybrid

composite were examined.

A pin-on-disk setup was used to investigate the dry sliding wear characteristics of the

friction stir welding of the aluminum metal matrix composites according to ASTM G99-

95 standards. The size of wear specimens was 4 mm diameter and length of 25 mm,

which were machined from the already taken samples of the nugget zone. The tests

were conducted at constant load of 50 N and a rotational speed of 1000 rpm. An

electronic digital balance with 0.1 mg accuracy was used to measure the initial and final

mass of the specimen. The masses of all specimens were measured before and after

running. The test was carried out for three hours, then the specimens were removed, from

the wear testing machine and cleaned with alcohol, in order to remove all the attached

worn particles, and then the mass of the specimen was measured to determine the mass

loss. The wear rates were determined using the volume loss method, as indicated by

equation 1, [17]:

s

MW

.ρ= , where (1)

W= volume loss during test period (cm3/m)

M = mass loss during wear test (g)

s = sliding distance (m)

ρ = density of the composite as computed from the rule of mixture = 2.7 g/cm3

3. RESULTS

3.1 Influence of the tool geometry on wear rate

The wear resistances of the friction stir welded composite joints were examined using

three different tool profiles (square, hexagonal, and octagonal). For every tool profile,

the wear tests were conducted at four different welding speeds (35, 45, 55, and 65)

mm/min, at different rotational speeds of 630, 800, 1000, and 1250 rpm. Figure 1 shows

the variation of the wear rate with welding speed for various tool pin profiles when the

rotational speed is maintained constant at 630, and 1250 rpm. The horizontal line shown

in Fig. 1 is drawn ONLY for the purpose of comparison between the as-cast base AMCs

and the welded zone. This line represents the nominal value of the wear rate at the base

AMCs measured at various points.

The results demonstrate that the tool geometry have significant influences on the wear

resistance of the welded joint, as obtained by ANOVA method [18]. In all considered

cases, the welded joints produced by the square pin profile tool exhibits superior wear

resistance to those joints welded by octagonal pin profile tools. The welded joints

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produced by hexagonal pin profile tool shows intermediate resistance values for wear.

Accordingly, it was decided to use the square head welding pin in all the following works

of this paper.

3.2 Influence of the rotational speed on wear rate

The effect of the rotational speed on the dry sliding wear resistance of the friction stir

welded joints of the considered composite was investigated using the square pin profile

tool, as mentioned earlier. The wear rates were measured at different rotational speeds

630, 800, 1000, and 1250 rpm, and at different constant welding (transverse) speeds of

35, 45, 55, 65 mm/min. The results, shown in Fig.2, indicate that the wear rate increases

with the increase in the rotational speed, for all the examined welding speeds. The joint

welded at 630 rpm, and 65 mm/min experiences the highest wear resistance among the

other examined specimens. However, ANOVA results indicate the changes of the wear

rate produced from different rotational speeds are not statistically significant [18].

3.3 Influence of the welding speed on wear rate

A set of experiments was conducted to measure the wear rate at different welding speeds

(35, 45, 55, and 65) mm/min, whilst keeping the rotational speed constant at 630, 800,

100, and 1250 rpm. Figure 3 shows the results obtained from the wear test. It seems that

the maximum wear rate of the welding zone was achieved by applying welding

(transverse) speed of 45 mm/min, with a rotational speed of 1250 rpm. The lower and

higher values of 45 mm/min cause a decrease in the wear rate of the weld zone. The

wear rate increased 6% due to an incremental increase of the transverse speed from 35

mm/min to 45 mm/min, respectively. When the transverse speed was raised from 45

mm/min to 65 mm/min, the wear rate decreased dramatically. The sample welded using

630 rpm and 65 mm/min shows the lowest wear rate among the other examined

specimens. In our previous study, ANOVA method shows that the variations of the wear

rate due to changes of the welding speed are statistically significant [18].

Accordingly, it can be said, that the wear rate decreases with the increase in welding

speed at constant rotational speed, and it increases with the increase in rotational speed at

constant welding speed.

4. DISCUSSION

4.1 Influence of the tool profile on wear rate

The results show that the wear resistance of the friction stir welded joint of the

considered composite is affected by the use of different tool pin profiles. The welded

joint produced by the square head shows the highest wear resistance. This could be

attributed to the mechanical stirring employed, and the total frictional heat input by

different tool pin profiles developed in the weld zone. Since the square pin cross-section

is the smallest among the other considered pin profile, when they are all drawn in the

same circle, so that less heat input will be developed in the weld zone, and thus, a fine

grained microstructure will form due to recrystallisation [19], further heat will cause

grain growth stage to occur during the recrystallization process, causing the formation of

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a coarser grain microstructure, when the other two profiles are used, which is consistent

with our findings as shown in Fig. 4, in which superior grain refinement is achieved upon

using square pin profile. The development of the fine structure will result in an increase

in the strength and hardness, and the weld zone will be more resistive to wear as stated by

Archrd’s law [20].


It was found that wear rate of the friction stir welded joints of the considered composite

increases with the increase in the rotational speed. This increase is a consequence of the

microstructure coarsening in the weld zone, as the process of recrystallisation occurs, due

to the relatively high frictional heat input generated at high rotational speed; this

coarsening effect is also observed in our experiments, where substantial grain refinement

in weld zone is obtained upon using low rotational speed, as shown in Fig. 5. It is

believed that the stage of grain growth will be reached during the recrystallization

process; due to the high temperature developed by increasing the rotational friction stir

welding speed leading to a relatively coarse grain microstructure. Also, the high stirring

rate will lead to the formation of some voids and cracks at the coarse matrix / SiC and

graphite particle interface [9], which assist the releasing and detaching of the

reinforcement particles during sliding conditions, causing the wear resistance to

deteriorate.


The dry sliding wear resistance of the friction stir welded joints of the composite is

improved by conducting the welding process at higher welding speed. This improvement

results from the reduction of the developed heat per unit area of the joints during welding

with the increase in the welding speed, and the increase in the cooling rate which leads to

the formation of a fine grain structure after recrystallisation, therefore hardness increases,

and the wear resistance improved. The change in the microstructure with the welding

speed is shown in Fig. 6. For example, the average grain size is reduced almost into half

of its size as the welding speed changes from 35 mm/min to 65 mm/min.

5. CONCLUSIONS

The present study investigated the influence of some process parameters of friction stir

welding Technique on the dry sliding wear characteristics of the considered hybrid

composite weld joint. The main conclusions are summarized as follows:

(1) The wear resistance of the friction stir welded joints is improved compared to the base

composite.

(2) The wear rate of the welded joint increases at high rotational speeds. The

microstructure coarsening is responsible on the reduction of the wear resistance of the

welded joints at high rotational speeds. Also, the high stirring rate will lead to the

formation of some voids and cracks at the coarse matrix / SiC and graphite particle

interface, which assist the releasing and the detaching of these particles during sliding

causing a reduction in the wear resistance of the composite.

(3) The welding speed has a great influence on the wear characteristics of the welded

joint. As the welding speed increases less heat will be encountered in the zone to be

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welded causing a fine grained microstructure to be formed. This will lead to an increase

in the strength, hardness and a reduction in wear rate of the weld zone.

(4) The dry sliding wear characteristics of the friction stir weld joint is affected by the pin

profile tool type, where the joints fabricated using the square pin profile tool reveals

higher resistance against wear than joints fabricated using either hexagonal or octagonal

pin profile tool. This tool profile induces less frictional heat than the other two profiles,

which, in turn, enhances fine grains structure formation, causing an increase in the

strength, hardness and the wear resistance of the welded joint.

ACKNOWLEDGEMENT

This work was supported by a grant from the Deanship of Scientific Research at

Jordan University of Science and Technology (Grant No. 2010/195). The authors also

would like to acknowledge all members of the Industrial Engineering Department

workshops and laboratories for their help in using the machines and other available

facilities.

REFERENCES 1. Suresha, S.; Sridhara, B.K. Effect of Addition of Graphite Particles on the Wear

Behavior in Aluminum-Silicon Carbide-Graphite Composites. Materials and Design

2010, 31(4), 1804-1812.

2. Suresha, S.; Sridhara, B.K. Effect of Silicon Carbide Particulates on Wear Resistance

of Graphite Aluminum Matrix Composites. Materials and Design 2010, 31(9), 4470-

4477.

3. Rao, R.N.; Das, S. Effect of SiC Content and Sliding Speed on the Wear Behavior of

Aluminum Matrix Composites. Materials and Design 2011, 32(2), 1066-1071.

4. Veeresh Kumar, G.B.; Rao, C.S.P.; Selvaraj, N.; Bhagyashekar, M.S. Studies on

Al6061-SiC and Al7075-Al2O3 Metal Matrix Composites. Journal of Minerals &

Materials Characterization & Engineering 2010, 9(1), 43-55.

5. Hayajneh, M.; Hassan, A.M.; Alrashdan, A.; Mayyas, A.T. Prediction of Tribological

Behavior of Aluminum-Copper Based Composite Using Artifical Neural Network.

Journal of Alloys and Compounds 2009, 470, 584-588.

6. Ellis, M.B.D. Joining of Aluminum Based Metal Matrix Composites. International

Material Reviews 1996, 41(2), 41-58.

7. Wert, J.A. Microstructures of Friction Stir Weld Joints Between an Aluminum-Base

Metal Matrix Composite and a Monolithic Aluminum Alloy. Scripta Materialia 2003,

49(6), 607-612.

8. Mishra, R.S.; Ma, Z.Y. Friction Stir Welding and Processing. Materials Science and

Engineering R 2005, 50 (1-78).

9. Sawla, S.; Das, S. Combined Effect of Reinforcement and Heat Treatment on the Two

Body Abrasive Wear of Aluminum Alloy and Aluminum Particle Composites. Wear

2004, 257(5-6), 555-561.

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10. Vijayan, S.; Raja, R.; Rao, S.R.K. Multiobjective Optimization of Friction Stir

Welding Process Parameters on Aluminum Alloy AA5083 Using Taguchi-Based Grey

Relation Analysis. Materials and Manufacturing Processes 2010, 25, 1206-1212.

11. Meran, C.; Canyurt, O.E. Friction Stir Welding of Austenitic Stainless Steel. Journal

of Achievements in Materials and Manufacturing Engineering 2010, 43(1), 432-439.

12. Aissani, M.; Gachi, S.; Boubenider, F.; Benkedda,Y. Design and Optimization of

Friction Stir Welding Tool. Materials and Manufacturing Processes 2010, 25, 1199-1205.

13. Suresh, C.N. Rajaprakas, B.M.; Upadhya, S. A Study of the Effect of Tool Pin

Profiles on Tensile Strength of Welded Joints Produced Using Frcition Stri Welding

Process. Materials and Manufacturing Processes 2011, 26(9), 1111-1116.

14. Kumar, K.; Kailas, S.V.; Srivatsan, T.S. The Role of Tool Design in Influencing the

Mechanism for the Formation of Friction Stir Welds in Aluminum Alloy 7020. Materials

and Manufacturing Processes 2011, 26(7), 915-921.

15. Yin, Y.H.; Sun, N.; North, T.H.; Hu, S.S. Influence of Tool Design on Mechanical

Properties of AZ31 Friction Stir Spot Welds. Science and Technology of Welding and

Joining 2010, 15(1), 81-87.

16.Prado, R.A.; Murr, L.E.; Soto, K.F.; McClure, J.C. Self Optimization in the Tool Wear

of Friction-Stir Welding of Al6061+20% Al2O3 MMC. Materials Science and

Engineering: A 2003, 349(1-2), 156-165.

17. Zhang, S.; Wang, F. Comparison of Friction and Wear Performances of Brake

Material Dry Sliding Friction Against Two Aluminum Matrix Composites Reinforced

with Different SiC Particles. Journal of Materials Processing Technology 2007, 182(1-3),

122-127.

18. Hassan, A.M., Almomani, M., Qasim, T., Ghaithan, A. Statistical Analysis of Some

Mechanical Properties of Friction Stir Welded Aluminum Matrix Composite Int. J.

Experimental Design and Process Optimisation 2012, 3 (1), 91–109.

19. Callister Jr., W.D.; Rethwisch, D.G. Materials Science and Engineering An

Introduction, 8th

ed. John Wiley and Sons, Inc., New York, 2010.

20. Archard, J.F.; Hirst, W. The Wear of Metals under Unlubirctaed Conditions.

Proceeding of the Royal Society of London. Series A, Mathematical and Physical

Sciences 1956, 236(1206), 397-410.

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00.00030.00060.00090.00120.00150.00180.00210.00240.00270.003

30 35 40 45 50 55 60 65 70

Welding speed (mm/min)

Wear rate (mm3/m)

Square pin

Hexagonal pin

Octagonal pin

00.00030.00060.00090.00120.00150.00180.00210.00240.00270.003

30 35 40 45 50 55 60 65 70


Wear rate (mm3/m)

Square pin

Hexagonal pin

Octagonal pin

Fig. 1. Wear rate (mm3/m) versus welding speeds (mm/min) for square, hexagonal, and

octagonal pin profiles at rotational speed: (a) 630 rpm (b) 1250 rpm.

(a)

(b)

Base material wear rate =

0.0027 mm3/m


0.0027 mm3/m

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0

0.0003

0.0006

0.0009

0.0012

0.0015

0.0018

0.0021

0.0024

0.0027

0.003

500 750 1000 1250 1500

Rotational speed (rpm)

Wear rate (mm3/m)

35 mm/min45 mm/min55 mm/min65 mm/min

Fig. 2. Wear rate (mm

3/m) versus rotational speed (rpm) at different welding speeds for

FSW AMCs welded joint [Square head pin tool].


0.0027 mm3/m

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0

0.0003

0.0006

0.0009

0.0012

0.0015

0.0018

0.0021

0.0024

0.0027

0.003

30 35 40 45 50 55 60 65 70


Wear rate (mm3/m)

630 rpm800 rpm1000 rpm1250 rpm

Fig. 3. Wear rate (mm3/m) versus welding speed (mm/min) at different rotational speeds

for FSW AMCs welded joints [Square head pin tool].


0.0027 mm3/m

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Medium Fine Large

Hexagonal Square Octagonal

Fig. 4 Effect of tool pin profiles on FSW zone microstructure using (a) Hexagonal, (b)

square, and (c) octagonal pin profile tools at rotational speed of 800 rpm and welding

(transverse) speed of 55 mm/min with magnification of 500X.

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Grain size

630 rpm 800 rpm 1000 rpm 1250 rpm

Fig. 5 Effect of rotational speed on the zone microstructure at rotational speed of 630,

800, 1000, 1250 rpm and welding (transverse) speed of 55 mm/min with magnification of

500X.

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Grain size

35 mm/min 45 mm /min 55 mm/min 65 mm/min

Fig. 6 Effect of welding (transverse) speed on the zone microstructure at welding

(transverse) speed of 35, 45, 55, 65 mm/min and rotational speed of 800 rpm with

magnification of 500X.

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Table 1

Chemical composition of the considered aluminum matrix composite

Cu Mg Si Fe Mn Ni Zn Ti Cr S C Al

0.02 3.95 0.88 0.72 0.02 0.08 <0.01 <0.01 0.19 0.008 0.418 93.694

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Table 2

Process parameters of friction stir welding

Pin Profile Tool Welding (transverse) speed (mm/min) Rotational Speed (rpm)

Square 35, 45 , 55, 65 630, 800, 1000, 1250

Hexagonal 35, 45 , 55, 65 630, 800, 1000, 1250

Octagonal 35, 45 , 55, 65 630, 800, 1000, 1250

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Processing Parameters Effect on Friction Stir Welded Aluminum Matrix

Composites Wear Behavior

Adel Mahmood Hassana*, Mohammed Almomani

a, Tarek Qasim

a, Ahmed

Ghaithana,

a Department of Industrial Engineering, Jordan University of Science and Technology. P.O. Box 3030,

Irbid 22110, Jordan.

ABSTRACT

In the present work, the aluminum matrix composites reinforced with both SiC and

graphite particles are joined using a friction stir welding (FSW) process. The wear

characteristics of the welded joints were investigated at constant load of 50 N and a

rotational speed of 1000 rpm using a pin-on-disk wear testing apparatus. This study

focuses on the influences of the FSW processing parameters (tool geometry, rotational

speed, and welding speed) on the wear characteristics of the welded joint of the

considered hybrid aluminum matrix composite under dry sliding conditions. The

experimental results indicate that the wear resistance of the joint increases at high

welding speeds (> 45 mm/min) and/or low value of rotational speeds. Different tool pin

profiles (square, octagonal, and hexagonal) are developed to perform the welding

process, and the effects of the tool pin profile on the weldments were studied. It is found

that joints welded with square pin profile have better wear resistance compared to the

other pin profiles. The results demonstrate that the FSW processing parameters greatly

affect on the wear resistance of the welded joints due to various microstructural

modifications during welding that cause an improvement in the welded zone hardness

and wear properties.

Keywords:

Aluminum; Composite; Friction; Welding; Wear

*Corresponding author Tel: +962-2-7201000, Ext: 22571

E-mail address: [email protected]

1. INTRODUCTION

At present, there is a continuously increasing demand for high strength and light weight

materials in transport and aerospace industries. These materials are more energy efficient

in terms of reducing fuel consumption. Aluminum matrix composite (AMCs) is one of

the promising candidate materials which have a great potential in the applications where

a weight reduction is critical [1,2]. They have outstanding attractive properties, i.e.

inexpensive, low specific density, high strength, good mechanical and wear properties

[3,4].

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Both fibers and particles reinforcement can be used in the aluminum matrix of AMCs.

SiC, Al2O3, SiO2, BN, and graphite are examples of the reinforcement particulates that

used commonly in AMCs [5]. Even though, the great advantages of the AMCs, the

difficulties associated with joining them together or with different materials using the

conventional fusion welding techniques limit their use in the industrial applications [6].

Fortunately, a new solid state joining process named as friction stir welding (FSW),

succeed to overcome many welding difficulties associated with the conventional fusion

welding processes [7]. Nowadays, welding and joining of AMCs to themselves or other

materials become possible and the market share for metal matrix composites (MMCs)

increased extensively [8].

Many of the products and the components made from AMCs are moving and sliding

parts, i.e. brake drums, cylinder blocks and drive shafts [9]. Due to the fact that the

production of these components involves the use of various secondary operations, i.e.,

machining, joining, etc. Then, it is very important to fully establish the wear

characteristics of the weld joint of AMCs in order to build a solid understanding of their

behavior in service condition.

The studies on the dry sliding wear behavior of aluminum alloys illustrate that the metal

matrix composites reinforced with hard particles are more resistive to wear than the

corresponding monolithic alloy [9]. It was observed that the addition of SiC particulate

to the aluminum matrix makes it harder, stronger, and more resistive to wear. This

increase in the hardness will be at the expense of machinability. Therefore, graphite

particles are used to maintain the gain achieved by SiC addition and concurrently

improve machining as well [1]. These considerations were an encouragement to select the

considered hybrid aluminum matrix composite with the two reinforcements particulate

(SiC and graphite) in the present study. Therefore, the present work differs from most

other earlier studies that focused on AMCs reinforced by only one type of reinforcement

by ceramics particles.

Optimization of the effect of the FSW processing parameters on the weld joint

performance has been of the interest of many researchers [10]. C. Meran and O.E.

Canyurt observed that fine grain structure formed at higher welding speeds due to a lower

heat input to the welding zone. In contrast, coarser grains generated at lower welding

speeds as a result of the increased heat input [11]. Furthermore, several researchers

studied the influence of the welding tool design parameters on the strength of the weld

joint [12-15].

Few researchers studied the wear resistance of FSW weld zone for Al based MMCs [16].

Hence, the present investigation is an attempt to assess the effect of the FSW processing

parameters (tool profile, rotational speed, and welding speed) on the wear resistance of

the considered welded hybrid composite joints under dry sliding conditions.

2. EXPERIMENTAL PROCEDURE

Plates of aluminum matrix composite with chemical composition shown in table 1 (100

mm x 75 mm x 7.5 mm) were butt friction stir welded using a special fixture. This

fixture was fixed firmly on the table of a conventional milling machine. The machine

spindle equipped with a welding tool. The working parameters used for friction stir

welding are shown in Table 2. Samples from the nugget zone of the friction stir welded

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plates were cut in a length of 25 mm in the welding direction and 20 mm in the transverse

direction. All samples were grounded with emery paper 800, and 1200 grit size, and

washed with water and alcohol to get rid off any left contamination.

Table 1

Chemical composition of the considered aluminum matrix composite

Cu Mg Si Fe Mn Ni Zn Ti Cr S C Al

0.02 3.95 0.88 0.72 0.02 0.08 <0.01 <0.01 0.19 0.008 0.418 93.694

Table 2

Process parameters of friction stir welding

Pin Profile Tool Welding (transverse) speed (mm/min) Rotational Speed (rpm)

Square 35, 45 , 55, 65 630, 800, 1000, 1250

Hexagonal 35, 45 , 55, 65 630, 800, 1000, 1250

Octagonal 35, 45 , 55, 65 630, 800, 1000, 1250

The effects of the FSW processing parameters (rotational speed, welding speed, and tool

pin profile) on the dry sliding wear rate of the welded zone of the considered hybrid

composite were examined.

A pin-on-disk setup was used to investigate the dry sliding wear characteristics of the

friction stir welding of the aluminum metal matrix composites according to ASTM G99-

95 standards. The size of wear specimens was 4 mm diameter and length of 25 mm,

which were machined from the already taken samples of the nugget zone. The tests

were conducted at constant load of 50 N and a rotational speed of 1000 rpm. An

electronic digital balance with 0.1 mg accuracy was used to measure the initial and final

mass of the specimen. The masses of all specimens were measured before and after

running. The test was carried out for three hours, then the specimens were removed, from

the wear testing machine and cleaned with alcohol, in order to remove all the attached

worn particles, and then the mass of the specimen was measured to determine the mass

loss. The wear rates were determined using the volume loss method, as indicated by

equation 1, [17]:

s

MW

.ρ= , where (1)

W= volume loss during test period (cm3/m)

M = mass loss during wear test (g)

s = sliding distance (m)

ρ = density of the composite as computed from the rule of mixture = 2.7 g/cm3

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3. RESULTS

3.1 Influence of the tool geometry on wear rate

The wear resistances of the friction stir welded composite joints were examined using

three different tool profiles (square, hexagonal, and octagonal). For every tool profile,

the wear tests were conducted at four different welding speeds (35, 45, 55, and 65)

mm/min, at different rotational speeds of 630, 800, 1000, and 1250 rpm. Figure 1 shows

the variation of the wear rate with welding speed for various tool pin profiles when the

rotational speed is maintained constant at 630, and 1250 rpm. The horizontal line shown

in Fig. 1 is drawn ONLY for the purpose of comparison between the as-cast base AMCs

and the welded zone. This line represents the nominal value of the wear rate at the base

AMCs measured at various points.

00.00030.00060.00090.00120.00150.00180.00210.00240.00270.003

30 35 40 45 50 55 60 65 70


Wear rate (mm3/m)

Square pin

Hexagonal pin

Octagonal pin

00.00030.00060.00090.00120.00150.00180.00210.00240.00270.003

30 35 40 45 50 55 60 65 70


Wear rate (mm3/m)

Square pin

Hexagonal pin

Octagonal pin

Fig. 1. Wear rate (mm3/m) versus welding speeds (mm/min) for square, hexagonal, and

octagonal pin profiles at rotational speed: (a) 630 rpm (b) 1250 rpm.

(a)

(b)


0.0027 mm3/m


0.0027 mm3/m

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The results demonstrate that the tool geometry have significant influences on the wear

resistance of the welded joint, as obtained by ANOVA method [18]. In all considered

cases, the welded joints produced by the square pin profile tool exhibits superior wear

resistance to those joints welded by octagonal pin profile tools. The welded joints

produced by hexagonal pin profile tool shows intermediate resistance values for wear.

Accordingly, it was decided to use the square head welding pin in all the following works

of this paper.


The effect of the rotational speed on the dry sliding wear resistance of the friction stir

welded joints of the considered composite was investigated using the square pin profile

tool, as mentioned earlier. The wear rates were measured at different rotational speeds

630, 800, 1000, and 1250 rpm, and at different constant welding (transverse) speeds of

35, 45, 55, 65 mm/min. The results, shown in Fig.2, indicate that the wear rate increases

with the increase in the rotational speed, for all the examined welding speeds. The joint

welded at 630 rpm, and 65 mm/min experiences the highest wear resistance among the

other examined specimens. However, ANOVA results indicate the changes of the wear

rate produced from different rotational speeds are not statistically significant [18].

0

0.0003

0.0006

0.0009

0.0012

0.0015

0.0018

0.0021

0.0024

0.0027

0.003

500 750 1000 1250 1500

Rotational speed (rpm)

Wear rate (mm3/m)

35 mm/min45 mm/min55 mm/min65 mm/min

Fig. 2. Wear rate (mm

3/m) versus rotational speed (rpm) at different welding speeds for

FSW AMCs welded joint [Square head pin tool].


A set of experiments was conducted to measure the wear rate at different welding speeds

(35, 45, 55, and 65) mm/min, whilst keeping the rotational speed constant at 630, 800,

100, and 1250 rpm. Figure 3 shows the results obtained from the wear test. It seems that

the maximum wear rate of the welding zone was achieved by applying welding

(transverse) speed of 45 mm/min, with a rotational speed of 1250 rpm. The lower and

higher values of 45 mm/min cause a decrease in the wear rate of the weld zone. The

wear rate increased 6% due to an incremental increase of the transverse speed from 35

mm/min to 45 mm/min, respectively. When the transverse speed was raised from 45

mm/min to 65 mm/min, the wear rate decreased dramatically. The sample welded using

630 rpm and 65 mm/min shows the lowest wear rate among the other examined


0.0027 mm3/m

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specimens. In our previous study, ANOVA method shows that the variations of the wear

rate due to changes of the welding speed are statistically significant [18].

0

0.0003

0.0006

0.0009

0.0012

0.0015

0.0018

0.0021

0.0024

0.0027

0.003

30 35 40 45 50 55 60 65 70


Wear rate (mm3/m)

630 rpm800 rpm1000 rpm1250 rpm

Fig. 3. Wear rate (mm3/m) versus welding speed (mm/min) at different rotational speeds

for FSW AMCs welded joints [Square head pin tool].

Accordingly, it can be said, that the wear rate decreases with the increase in welding

speed at constant rotational speed, and it increases with the increase in rotational speed at

constant welding speed.

4. DISCUSSION

4.1 Influence of the tool profile on wear rate

The results show that the wear resistance of the friction stir welded joint of the

considered composite is affected by the use of different tool pin profiles. The welded

joint produced by the square head shows the highest wear resistance. This could be

attributed to the mechanical stirring employed, and the total frictional heat input by

different tool pin profiles developed in the weld zone. Since the square pin cross-section

is the smallest among the other considered pin profile, when they are all drawn in the

same circle, so that less heat input will be developed in the weld zone, and thus, a fine

grained microstructure will form due to recrystallisation [19], further heat will cause

grain growth stage to occur during the recrystallization process, causing the formation of

a coarser grain microstructure, when the other two profiles are used, which is consistent

with our findings as shown in Fig. 4, in which superior grain refinement is achieved upon

using square pin profile. The development of the fine structure will result in an increase

in the strength and hardness, and the weld zone will be more resistive to wear as stated by

Archrd’s law [20].


0.0027 mm3/m

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Medium Fine Large

Hexagonal Square Octagonal

Fig. 4 Effect of tool pin profiles on FSW zone microstructure using (a) Hexagonal, (b)

square, and (c) octagonal pin profile tools at rotational speed of 800 rpm and welding

(transverse) speed of 55 mm/min with magnification of 500X.


It was found that wear rate of the friction stir welded joints of the considered composite

increases with the increase in the rotational speed. This increase is a consequence of the

microstructure coarsening in the weld zone, as the process of recrystallisation occurs, due

to the relatively high frictional heat input generated at high rotational speed; this

coarsening effect is also observed in our experiments, where substantial grain refinement

in weld zone is obtained upon using low rotational speed, as shown in Fig. 5. It is

believed that the stage of grain growth will be reached during the recrystallization

process; due to the high temperature developed by increasing the rotational friction stir

welding speed leading to a relatively coarse grain microstructure. Also, the high stirring

rate will lead to the formation of some voids and cracks at the coarse matrix / SiC and

graphite particle interface [9], which assist the releasing and detaching of the

reinforcement particles during sliding conditions, causing the wear resistance to

deteriorate. Grain size

630 rpm 800 rpm 1000 rpm 1250 rpm

Fig. 5 Effect of rotational speed on the zone microstructure at rotational speed of 630,

800, 1000, 1250 rpm and welding (transverse) speed of 55 mm/min with magnification of

500X.


The dry sliding wear resistance of the friction stir welded joints of the composite is

improved by conducting the welding process at higher welding speed. This improvement

results from the reduction of the developed heat per unit area of the joints during welding

with the increase in the welding speed, and the increase in the cooling rate which leads to

the formation of a fine grain structure after recrystallisation, therefore hardness increases,

and the wear resistance improved. The change in the microstructure with the welding

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speed is shown in Fig. 6. For example, the average grain size is reduced almost into half

of its size as the welding speed changes from 35 mm/min to 65 mm/min.

Grain size

35 mm/min 45 mm /min 55 mm/min 65 mm/min

Fig. 6 Effect of welding (transverse) speed on the zone microstructure at welding

(transverse) speed of 35, 45, 55, 65 mm/min and rotational speed of 800 rpm with

magnification of 500X.

5. CONCLUSIONS

The present study investigated the influence of some process parameters of friction stir

welding Technique on the dry sliding wear characteristics of the considered hybrid

composite weld joint. The main conclusions are summarized as follows:

(1) The wear resistance of the friction stir welded joints is improved compared to the base

composite.

(2) The wear rate of the welded joint increases at high rotational speeds. The

microstructure coarsening is responsible on the reduction of the wear resistance of the

welded joints at high rotational speeds. Also, the high stirring rate will lead to the

formation of some voids and cracks at the coarse matrix / SiC and graphite particle

interface, which assist the releasing and the detaching of these particles during sliding

causing a reduction in the wear resistance of the composite.

(3) The welding speed has a great influence on the wear characteristics of the welded

joint. As the welding speed increases less heat will be encountered in the zone to be

welded causing a fine grained microstructure to be formed. This will lead to an increase

in the strength, hardness and a reduction in wear rate of the weld zone.

(4) The dry sliding wear characteristics of the friction stir weld joint is affected by the pin

profile tool type, where the joints fabricated using the square pin profile tool reveals

higher resistance against wear than joints fabricated using either hexagonal or octagonal

pin profile tool. This tool profile induces less frictional heat than the other two profiles,

which, in turn, enhances fine grains structure formation, causing an increase in the

strength, hardness and the wear resistance of the welded joint.

ACKNOWLEDGEMENT

This work was supported by a grant from the Deanship of Scientific Research at

Jordan University of Science and Technology (Grant No. 2010/195). The authors also

would like to acknowledge all members of the Industrial Engineering Department

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workshops and laboratories for their help in using the machines and other available

facilities.

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