Alloy Designation System

• Wrought aluminium alloys were standarized by Aluminium Association in 1954.

X X X X

Alloy Group

Impurity Limit Min. Al % after decimal point

1060: 1xxx series having 99.60% Al.

2

Designation Table

1xxx Al, more than 99% pure

2xxx Copper

3xxx Manganese

4xxx Silicon

5xxx Magnesium

6xxx Magnesium and Silicon

7xxx Zinc

8xxx Other elements

3

Temper Designation-I

Five basic tempers: F denotes as Fabricated; O denotes annealed, Recrystallized; H denotes strained hardened; T for heat treated and W as Solution heat treated

F: Tempering done by normal manufacturing process.

O: The softest temper

H: Mechanical properties increased by cold working. Hxyz: H1yz: Strained hardened only. H2yz: Strain hardened and partially annealed - Purpose???H3yz: Strained hardened and stabilized – Purpose???

y: Amount of cold workingH18z: Full hardened;H14z: Half hardened

z: identifies a special set of mechanical properties

AV-485

4

Temper Designation-IIW: Alloys which spontaneously age at RT after solution treatment. T: Thermally treated with or without supplementary SH. Produces stable tempers. Followed by numbers from 2 to 10.

T2: Annealed for cast products onlyT3: Solution heat-treated and then cold worked

T4: Solution heat treated and naturally aged to stable state

T5: Artificially agedT6: Solution heat treated and artificially agedT7: Solution treated and then stabilizedT8: Solution treated, cold worked and then artificially aged

T9: Solution treated, artificially aged and then cold workedT10: Artificially aged and then cold worked

5

Aluminium Copper (2xxx)-I

Interesting reading from AVp485

Simple Phase Diagrams

300

350

400

450

500

550

600

650

700

0 10 20 30 40 50 60

wt.% Mg

Tem

pe

ratu

re (

C)

Liquid

Liquid + -Al

-Al

-Al + -AlMg

-A

lMg

-AlMg

-A

lMg

Al-Mg System (Al-Rich)

300

400

500

600

700

800

900

1000

1100

1200

0 20 40 60 80 100

wt.% Mg

Tem

per

atu

re (

C)

Liquid

Liquid + Mg

CuMg2 + Mg

CuM

g2

L + CuMg2

L + -Cu

Laves - C15

-Cu +

Laves - C15

Liquid + Laves - C15

Cu-Mg System

Ternary Phases S - Al2CuMg, T - Mg32(Al,Cu)49, V - Al5Cu6Mg2, Q - Al7Cu3Mg6

Even for simple 2xxx alloy (Al-Cu-Mg), need data for 3 binaries and information about ternary phases

400

450

500

550

600

650

700

0 10 20 30 40 50 60wt.% Cu

Tem

per

atu

re (

C)

Liquid

Liquid + -Al

-Al

Liquid + -Al2Cu

-Al + -Al2Cu-Al2Cu

Al-Cu System (Al-Rich)

MTDATA predicted phase diagrams

Real, commercial Al-alloys may contain > 10 alloying elements!See HDB-Al1-pdf

Solidification MicrostructuresSolidification occurs rapidly under non-equilibrium conditions

However, given certain assumptions, thermodynamic calculations and the equilibrium phase diagram can still be used to predict solidification microstructure

Scheil Solidication Model - Assumptions:

(i) Local equilibrium exists at the solid/liquid interface

(ii) No diffusion in the solid phases

(iii) Uniform liquid composition

(iv) No density difference between

solid and liquid

% Solute

T

Cliq1

Csol1Cliq2

Csol2Cliq3

Csol3

C0

Csol0

Liquid

Solid

Microstructure

Cast SolutionizedHomogenized Rolled

RD

Microstructural ChangesT

em

pe

ratu

re

Aged

Time

50nm

13

Aluminium Copper (2xxx)-IIDuralumin -2017 oldest of all heat-treatable aluminium alloys having 4% Cu. Widely used for aircraft construction.

NA alloy – has to be refrigerated after solution treatment – Good formability in the solution treated condition – subsequent precipitation increases the strength and hardness.

2014 has higher Cu and Mn content and susceptible to artificial ageing. In artificially aged condition 2014 has higher YS, TS but lower elongation than 2017.

2024 with 4.5%Cu and 1.5% Mg highest strength of any NA 2xxx series. Mainly used for aircraft structures, rivets, hardware, truck wheels and screw machine products.

14

Aluminium Copper (2xxx)-IIIAdding of Mg reduces the formability and makes it more difficult to fabricate.

Increase of silicon in cast alloy increases the fluidity and hence thin sectioned castings are made with ease.

15

Aluminium Manganese (3xxx)-I

AVp489

β + L

α + β α

L

α + L 660 C

1 2 4

Although solubility decreases with decreasing temperature, not age hardened – why?

16

Aluminium Manganese (3xxx)-II

Not used as major alloying elements in any casting alloy, used only for wrought alloys.

3003 – good formability, corrosion res. And good weldability. Used as utensils, storage for food, oil, gasoline and pr. vessels.

beverage cans (3XXX) Al-Mn or Al-Mn-Mg

17

Aluminium Silicon (4xxx)-I

AVp489

18

Aluminium Silicon (4xxx)-II

Have excellent castability and resistance to corrosion. Typical use for intricate casting and marine fittings.

4032 containing 12.5% Si used for automotive pistons owing to its low coeff. of thermal expansion and good forgeability.

19

Aluminium Magnesium (5xxx)-I

20

Aluminium Magnesium (5xxx)-II

Good weldability, Corrosion resistance and moderate strength.

5005 (0.8%Mg): architectural extrusions;

5050 (1.2% Mg): automotive gas and oil lines;

5052 (2.5% Mg): aircraft fuel and gas lines

5083 (4.5% Mg): marine and welded structural applications

22

Al-Mg-Si (6xxx)-I

23

Al-Mg-Si (6xxx)-II

More workable than other heat treatable alloys. Excellent corrosion resistance. Automobile body, furniture, vacuum cleaner turbine and architectural applications.

24

Al-Zn (7xxx)-I

Put phase diagram from Internet and explain from AVp492

Dispersoids

• Fine Al3Zr dispersoid particles precipitate during homogenization of 7050

• Dispersoid particles are important for the control of grain structure during processing– Act to “pin” grain boundaries

Al3Zr dispersoid particles in 7050 after homogenization

26

Al-Zn (7xxx)-II

7075 and 7079 produce highest tensile strength obtainable in aluminium alloys.

Used where high strength and good corr. res is required. Aircraft structural parts.

Some Issues

• Automotive Applications

• Corrosion Resistance

• Precipitation Hardening

• Strain Hardening

28

Automotive Applications

Low C SteelExcellent formability at RTGood surface finishLow cost

Al alloysFormability at RT 2/3 of Steel

Warm forming with 5xxx and 6xxx alloys

5xxxExhibit higher strength BUT suffers from Ludering

6xxxHave the advantage of pptn hardening after forming

Aluminium Alloys in Aerospace

2XXX (Cu-containing, 500 MPa)

7XXX (Zn+Mg+Cu-containing, 600 MPa)

Design Requirements

• Components must be– Lightweight– Damage tolerant– Durable (corrosion resistant)– Cost effective

• Requires careful balance of material properties

Critical Material Properties

Aluminium Alloys• Pure aluminium has

– Low density (relative

Al=2.7, Fe=7.9)

– Readily available (Al is 3rd most abundant element in Earth's crust)

– Highly formable (FCC crystal structure)

– Low strength and stiffness (EAl

=70GPa, EFe

=211GPa)

– Low melting point (Tm=660oC)

• Alloy with other elements to improve strength and stiffness - results in alloys with properties well matched to aerospace requirements

Aerospace Al-Alloys• Dominated by “high strength” wrought alloys

• Two main alloy series in particular – 2xxx alloys (Al + Cu, Mg) UTS~500MPa– 7xxx alloys (Al + Mg, Zn, (Cu)) UTS~600MPa

A) Slats - 2618B) D-Nose Skins - 2024C) Top Panel - 7150D) Bottom Panel - 2024

E) Spars / Ribs - 7010F) Flap Support - 7175G) Flap Track - 7075H) Landing Gear - 2024

A

BC

E

D

FG

H

Alloys used in typical wing structure

Next Generation Aircraft

Bigger....

...FasterBoeing sonic cruiser > Mach.95

Airbus A380 > 950 seats

Goals

• Next generation aircraft rely on advances in materials and assembly methods

• Weight reduction is critical– Alloy optimization

• Increase strength and stiffness and/or reduce density whilst maintaining other properties

– Assembly optimization• Reduce weight associated with joints between

components

Alloy Design

• Traditionally, alloy and process development largely by trial and error based on metallurgical experience

• Recently, emphasis has changed to designing alloys and processes to meet specific property goals– Improved understanding of relationships between

processing, microstructure and properties– Development of models to predict alloy microstructure and

performance

Questions1. Discuss how micro alloying influences the precipitation reactions in

aluminium alloys? Polmear P49.

2. Principle of formation of PFZ and its role in controlling mechanical properties

3. Dislocation precipitate interaction and its effect on strength and work hardening

4. Notes on Non-Heat treatable Aluminium Alloys. Polmear 130

5. Notes on 2XXX alloys – consider both cast and wrought

6. Notes on 6xxx alloys - consider both cast and wrought

7. Alloy design and properties for Aircraft alloys

8. Alloy design and properties for Automotive sheets and structural alloys

9. Alloy design and properties for Shipping

10. Alloy design and properties for Superplastic alloys