Metal Alloys

Lecture 15 Dr Greg Heness

How can you tell others exactly which kind of material you

want?

What do these codes mean?

AISI 1020 steel

ASTM A 29 grade 1020 steel

UNS G10200

SAE 1006

6061-T6

3003-H38

� Some Specifications applicable to Steel Products and

other Metals

� Steels

� Effect on strength

� The Most Widely Used System for Designating Steels SAE-

AISI

� Wrought Aluminium Alloys – Aluminum Association

designation system

� Cast Aluminium Alloy Designations

Some Specifications applicable to Steel Products and other Metals

AS Standards AustraliaStandards AustraliaStandards AustraliaStandards Australia

SAESAESAESAE----AISIAISIAISIAISI Society of Automotive Engineers Society of Automotive Engineers Society of Automotive Engineers Society of Automotive Engineers –––– American American American American Iron and Steel InstituteIron and Steel InstituteIron and Steel InstituteIron and Steel Institute

ASTMASTMASTMASTM(UNS)(UNS)(UNS)(UNS)

American Society for Testing and Materials American Society for Testing and Materials American Society for Testing and Materials American Society for Testing and Materials ((((www.astm.orgwww.astm.orgwww.astm.orgwww.astm.org))))

ASMEASMEASMEASME American Society of Mechanical EngineersAmerican Society of Mechanical EngineersAmerican Society of Mechanical EngineersAmerican Society of Mechanical EngineersMILMILMILMIL U.S. Department of DefenseU.S. Department of DefenseU.S. Department of DefenseU.S. Department of DefenseAMSAMSAMSAMS Aerospace Materials SpecificationAerospace Materials SpecificationAerospace Materials SpecificationAerospace Materials SpecificationBSBSBSBS British Standards InstitutionBritish Standards InstitutionBritish Standards InstitutionBritish Standards Institution

((((http://www.bsi-global.com/index.xalter))))EN EN EN EN European Committee for Standardization European Committee for Standardization European Committee for Standardization European Committee for Standardization

((((http://www.cenorm.behttp://www.cenorm.behttp://www.cenorm.behttp://www.cenorm.be))))

� Introduction to Aluminium alloys

� Unified Numbering System (UNS)

Developed by ASTM and SAE

Not a specification but only identify an alloy covered by other

standards

The 5 digits closely related to the original identification

system. E.g. AISI 1020 = G10200

Adopted by the Copper Development Association as official

identification system for Cu alloys

�Ferrous Alloys

� Classifications of Steel

� Anneaing

The benefits of annealing are:

Improved ductility

Removal of residual stresses that result from cold-

working or machining

Improved machinability

Grain refinement

� Spheroidizing

Hypereutectoid steels consist of pearlite and

cementite.

This presents difficulty in machining the

hypereutectoid steels.

This structure is desirable when minimum hardness,

maximum ductility and maximum machinability are

required

� Types of Steel

Low Carbon Steel

Medium Carbon Steel

High Carbon Steel

Yield Strengths Ranges of Steels

� Cast Iron

White: Hard and brittle, good wear resistance

Uses: rolling & crunching equipment

Grey: Good compressive & tensile strength, machinability,

and vibration-damping ability

Uses: machine bases, crankshafts, furnace doors,

Engine blocks

Most Frequently Used Carbon and Alloy Steels

SAE 1010: formed sheet-metal parts

SAE 1020: general machine applications

SAE 1040: flame- or induction-hardened parts

ASTM A36: structural steel

SAE 4140: high-strength machine parts

SAE 4340: high-strength machine parts

SAE 8620: carburized wear parts

Stainless Steels Ferritic

very formable, relatively weak; used in architectural trim,

kitchen range hoods, jewelry, decorations, utensils Grades

409, 430, and other 400

Austentitic

non-magnetic, machinable, weldable, relatively weak; used in

architectural products, such as fascias, curtain walls,

storefronts, doors & windows, railings; chemical processing,

food utensils, kitchen applications.

Grades 301, 302, 303, 304, 316, and other 300 series.

Martensitic

High strength, hardness, resistance to abrasion; used in

turbine parts, bearings, knives, cutlery and generally

Magnetic. Grades 17-4, 410, 416, 420, 440 and other 400

series

Maraging (super alloys):

High strength, high temperature alloy used in structural

applications, aircraft components and are generally magnetic.

Alloys containing around 18% Nickel.

A Repertoire of Stainless Steels

Type Uses

303

S30300

For fasteners and shafts where only rust or splash and spill resistance are needed

304/L All types of chemical immersion

316/L All types of chemical immersion where 304 is not adequate

17-4 PHS17400

High stress fasteners, shafting, agitators and machine supports; age hardened

17-7 PH

S17700

Harden to condition CH900 for chemical-resistant springs

A Repertoire of Stainless Steels

Type Uses

430S43000

For rust resistance on decorative an nonfunctional parts

416S41600

Hardened to 30 HRC and use for jigs, fixtures and base plates

420S42000

Harden to 50-52 HRC for tools that do not require high wear resistance (e.g. injection-molding cavities, nozzles, holding blocks, etc)

440C

S44004

Harden to 58-60 HRC for cutting devices, punches and dies

Aluminium Alloys

� Al alloys & treatment classification system

Examples

3003-H18: 3003 alloy cold finished to full hard temper

6061-T6: 6061 alloy, solution heat treated and furnace aged

hardened.

Most commonly used Aluminium alloys

Wrought alloys Sand Cast

1100 (pure Al) 355.0*

2024*

3003

5052 Die Cast

6061* 380.0

6063*

7075*

6xxx Series

Al-Mg-Si

Medium strength structural alloys. Weldable, corrosion

resistant, no stress corrosion cracking

Mg2Si is strengthening precipitate

One Use!!

A380 actually fastened together!

A crack size of 1.5 mm is assumed

100,000 fatigue cracks in A300

About 10% of all fastener holes

Al alloys, 2024 for toughness

7150-T351 for stiffness

� Al – Li alloys – “8000” series

Rationale:

Li is light – density 540 kg m-3

Reduces alloy density by 1% for each 1% Li

Li dissolves up to 14% in Al at high T

Solubility drops at lower temps

Can harden via the metastable δ` phase Al3Li – though

this only has low strains around it.

Li has big size difference: good solid soln strengthener

Li raises E of alloy: 10%Li gives 20% boost in E

� Problems ?

Li oxidises rapidly – needs careful handling

Severe gravity segregation during casting

Na, K, present as impurities form low m.p. phases

grain boundary failures

Simple Al-Li binary alloys have poor properties

cutting of δ` ppts ⇒ planar slip ⇒ low ductility

Overaging gives precipitation of δ phase at grain

boundaries

High cost – about 2-3x conventional alloys

Copper Alloys

Density; 8.93 g/cc so alloys are heavier than steel.

Specific strength not very high

Good ductility, (very soft when pure).

Corrosion resistant (some surface reactions)

Relatively good fatigue, creep and wear resistance compared

to Al alloys.

High electrical and thermal conductivity.

Easily joined and fabricated.

� Strengthening:

Cold-working: principle method for most alloys

Solid solution:- Cu-Zn, Cu-Sn, Cu-Al, Cu-Be

Age-hardenable:- Cu-Zr, Cu-Be

Phase transformations:- Cu-Al

Copper Alloys

Strength and hardness of copper is relatively low; to improve

strength, copper is frequently alloyed

Bronze - alloy of copper and tin (typically . 90% Cu, 10% Sn),

widely used today and in ancient times (i.e., the Bronze Age)

– Additional bronzes include aluminum bronzes and

silicon bronzes

Brass - alloy of copper and zinc (typically . 65% Cu, 35% Zn).

Highest strength alloy is beryllium-copper (only about 2% Be),

which can be heat treated to high strengths and used for

springs

Includes both wrought and cast copper and its alloys

Examples

C10100 – 99.99% pure copper

C17000 – 98% Cu, 1.7% Be (beryllium-copper)

C24000 – 80% Cu, 20% Zn (brass)

C52100 – 92% Cu, 8% Sn (bronze)

Brasses Cu-Zn alloys

Several phases: α (FCC) - soft, ductile, easily cold-worked.

β’ is BCC, harder & stronger than .

60-40 brass is (α + β’)

Brasses

o Admiralty brass contains 30% zinc and 1% tin which inhibits

dezincification in most environments.

o Alpha brasses (Prince's metal), with less than 35% zinc, are

malleable, can be worked cold, and are used in pressing,

forging, or similar applications. They contain only one

phase, with face-centered cubic crystal structure.

o Alpha-beta brass (Munz metal), also called duplex brass, is

35-45% zinc and is suited for hot working. It contains both α

and β' phase; the β'-phase is body-centered cubic and is

harder and stronger than α. Alpha-beta brasses are usually

worked hot.

o Aluminium brass contains aluminium, which improves its

corrosion resistance. Used in Euro coins (Nordic gold).

o Arsenical brass contains an addition of arsenic and

frequently aluminium and is used for boiler fireboxes.

o Beta brasses, with 45-50% zinc content, can only be worked

hot, and are harder, stronger, and suitable for casting.

o Cartridge brass is a 30% zinc brass with good cold working

properties.

o Common brass, or rivet brass, is a 37% zinc brass, cheap

and standard for cold working.

o DZR brass is Dezincification resistant Brass with a small

percentage of Arsenic.

o Gilding metal is the softest type of brass commonly

available. An alloy of 95% copper and 5% zinc, gilding metal

is typically used for ammunition components.

o High brass, contains 65% copper and 35% zinc, has a high

tensile strength and is used for springs, screws, rivets.

o

Brasses Cu-Zn alloys

� Several phases: α (FCC) - soft, ductile, easily cold-worked.

� β’ is BCC, harder & stronger than α.

� 60-40 brass is (α + β’)

o Leaded brass is an alpha-beta brass with an addition of

lead. It has excellent machinability.

o Low brass is a copper-zinc alloy containing 20% zinc with a

light golden color, excellent ductility and is used for flexible

metal hoses and metal bellows.

o Naval brass, similar to admiralty brass, is a 40% zinc brass

and 1% tin.

o Red brass, while not technically brass, is an American term

for CuZnSn alloy known as gunmetal.

o Rich low brass contains 85% copper 15% zinc often used in

jewellery applications .

o White brass contains more than 50% zinc and is too brittle

for general use.

o Yellow brass is an American term for 33% zinc brass.

Bronzes Cu + Sn, Al, Si, Ni

Stronger than brasses and still good corrosion resistance.

Precipitation hardenable - e.g. Cu-Be - very high strength,

corrosion & wear resistant…. etc.

Element Atomic Radius

Cu 0.1278

Zn 0.1332

Sn 0.1510

Magnesium

o Very low density: 1.74 Mg/m3 (Al: 2.7)

o relatively soft

o low E (45GPa)

o BUT

o Expensive,

o Difficult to cast,

o Low strength,

o Low creep, fatigue and wear resistance

o Low room temp. ductility (hcp) so cold-working

limited.

o Fabricated by casting - (melts at 651°C) or hot-working

(200-350°C).

o Used for weight saving applications; Missiles, luggage,

laptops, cellphones, chainsaws, cameras….

Miscellaneous Nonferrous Alloys

Zinc:

o unalloyed zinc also is a relatively soft metal having a

low melting temperature and a subambient

recrystallization temperature.

o Susceptible to corrosion.

o Galvanized steel (the zinc preferentially corrodes and

protects the steel.)

o Common applications of zinc alloys include die-castings

- padlocks, automotive parts (door handles and grilles),

and office equipment.

Titanium and Its Alloys

o Medium density 4.54 Mg/m3 (steel 7.9 Mg/m3)

o High melting point (1668°C)

o But relatively strong. Yiled 800 MPa (max . 1100 MPa)

o Stiffer than Aluminium; 107 - 116 GPa vs 70 GPa but

not as stiff as steel (207 GPa).

o Highly ductile

o Good corrosion resistance

o Good strength to weight ratio

o Expensive production due to reactivity at high

temperature.

o Almost all Ti contains aluminum

o increases ductility

o reduced density

Miscellaneous Nonferrous Alloys Lead, tin and their alloys

o Both are mechanically soft and weak,

o have low melting temperatures,

o are quite resistant to many corrosion environments,

o and have recrystallization temperatures below room

temperature.

o Many solders are lead-tin alloys.

o Lead & alloys - x-ray shields and storage batteries.

o Tin - a very thin coating on plain carbon steel

Nickel and Its Alloys

o Superalloys

o •High temperature performance (strength)

o Gas turbines, steam turbines, reciprocating engines

o Hot working and casting tools and dies

o Aircraft & space vehicles

o Nuclear and chemical industries

o Iron based alloys:

o 32% to 67% Fe, 15% to 22% Cr and 9% to 38% Ni.

o - common alloys: Incoloy series

o Cobalt based alloys:

o - 30% to 65% Co, 19% to 30% Cr and up to 35% Ni.

o - they retain their strength at high temp. but not as

strong as Ni-base superalloys

o Nickel based alloys:

o - 38% to 76% Ni, up to 27% Cr and 20% Co.

o - are the most common superalloys

� common alloys: Hastelloy, Inconel, Nimonic, Rene and

Astroloy series

20

• Steels: increase TS, Hardness (and cost) by adding

--C (low alloy steels)

--Cr, V, Ni, Mo, W (high alloy steels)

--ductility usually decreases w/additions.

• Non-ferrous:

--Cu, Al, Ti, Mg, Refractory, and noble metals.

• Fabrication techniques:

--forming, casting, joining.

• Hardenability

--increases with alloy content.

• Precipitation hardening

--effective means to increase strength in

Al, Cu, and Mg alloys.

SUMMARY

NonFerrous Alloys

• Cu AlloysBrass: Zn is subst. impurity (costume jewelry, coins, corrosion resistant)Bronze: Sn, Al, Si, Ni are subst. impurity (bushings, landing gear)Cu-Be: precip. hardened for strength

• Al Alloys-lower ρ: 2.7g/cm3 -Cu, Mg, Si, Mn, Zn additions -solid sol. or precip. strengthened (struct. aircraft parts & packaging)

• Mg Alloys-very low ρ: 1.7g/cm3 -ignites easily -aircraft, missles

• Refractory metals-high melting T -Nb, Mo, W, Ta• Noble metals

-Ag, Au, Pt -oxid./corr. resistant

• Ti Alloys-lower ρ: 4.5g/cm3 vs 7.9 for steel -reactive at high T -space applic.

SteelsSAE - AISI Number Classification

1XXX Carbon steelsLow carbon steels: 0 to 0.25 % CMedium carbon steels: 0.25 to 0.55 % CHigh carbon steels: Above 0.55 % Carbon

2XXX Nickel steels5 % Nickel increases the tensile strength without reducing ductility.8 to 12 % Nickel increases the resistance to low temperature impact15 to 25 % Nickel (along with Al, Cu and Co) develop high magnetic properties. (Alnicometals)25 to 35 % Nickel create resistance to corrosion at elevated temperatures.

3XXX Nickel-chromium steelsThese steels are tough and ductile and exhibit high wear resistance , hardenability and high

resistance to corrosion.

4XXX Molybdenum steelsMolybdenum is a strong carbide former. It has a strong effect on hardenability and high

temperature hardness. Molybdenum also increases the tensile strength of low carbon steels.

5XXX Chromium steelsChromium is a ferrite strengthener in low carbon steels. It increases the core toughness and the

wear resistnace of the case in carburized steels.

86XX87XX93XX94XX97XX98XX

Triple Alloy steels which include Nickel (Ni), Chromium (Cr), and Molybdenum (Mo).These steels exhibit high strength and also high strength to weight ratio, good corrosion resistance.