The document discusses aluminum-lithium alloys, including their production, properties, strengthening mechanisms, and applications. Key points include: - Aluminum-lithium alloys have high strength and stiffness but low density due to lithium's low density and high solubility in aluminum. - Precipitation strengthening occurs through the formation of coherent spherical δ' (Al3Li) precipitates during aging, improving strength. - Adding elements like Cu, Mg, and Zr can improve ductility and toughness by reducing strain localization and minimizing precipitate-free zones. - Aluminum-lithium alloys are used in aircraft for components like wings and fuselages

1. METALLURGY OF ALUMINIUM-LITHUM
ALLOY
By:-
Mr. K M Varun

2. Introduction
• Availability, specific strength, low density, good mechanical properties
etc…
• Wrought aluminum – 70%
• Imp. role in aerospace manufacturing.

3. Al production & properties
• Ore – Bauxite
• Production :- (a) Bayer’s process
(b) Hall-Heroult process
(c) Refining process
• Mechanical and chemical properties.

4. Al alloy systems
• Cu, Si, Zn, Mg, Fe, Mn, Ni, Li etc..
• Groups:-
(a) Wrought non heat treatable
(b) Wrought heat treatable
(c) Cast
• Designation :-

5. Wrought alloys

6. Cast alloys

7. Physical Metallurgy
• Concerns :-
(a) Composition effect
(b) Mechanical working &/or HT effect on physical
& mechanical properties.
• Phases in Al alloys –
oGood solid solubility:- Zn, Cu, Mg, Mn, Ag, Li etc.
oSolubility increases with temp.
oSecondary phases
Solid solubility of Li in Al > 10%

8. • Equilibrium binary solid solubility as a function of temp. for alloying
elements most frequently added to Al.

9. Strengthening Mechanism
• Objective – Increase strength, hardness, resistance to
wear, creep & fatigue prop.
• Strengthening in Non heat treatable alloys:-
Solid solution (Mg & Mn), Secondary phases( Si, Fe,
Cr) grain refinement(Zr, Ti), strain hardening
• Strengthening by HT:-
Precipitation strengthening – Li, Cu, Zn

10. WhyAl-Li alloy?
• Increasing payload & fuel efficiency – Aerospace
industry.
• More promising than 2xxx & 7xxx Al alloys & C fiber
composites.
• CFRP etc.. - costly
• Structural wt. reduction
• Cryogenic application

11. Effect of Li addition
• Substantial solid solubility in Al – 4.2% at 600˚C.
• Low density of Li – 0.54g/cm3 (At wt. of Li-6.94 & Al-26.98)
• Increase in Young’s modulus & specific modulus
• Higher specific modulus reduces the rate of fatigue crack growth
• Resistance to exfoliation corrosion & stress corrosion cracking.
• Improved thermal stability.

14. Phase Diagram
α

15. Precipitation strengthening
• Solution HT followed by thermal aging.
• Formation of spherical δ' (Al3Li) precipitates.
• Precipitate structure – quenching rate, cold working
before aging, aging temp. & time.
• Size & volume fraction of precipitates – comp. & temp.
• Effect of minor alloying element (graph)

17. Zones in PS

18. • Schematic depiction of several stages in the formation of the equilibrium precipitate () phase.
(a) A supersaturated solid solution. (b) A transition, , precipitate phase. (c) The equilibrium
phase, within the -matrix phase.
Li

19. • Effect of minor additions (0.15 wt%) of cadmium, iridium, and tin on
the age-hardening response of aluminum-lithium alloy 2090 (2.3 Cu,
2.3 Li, 0.15 Zr)

20. Al-Li alloys
• Geometrical similarity & lattice parameters b/w precipitates & FCC solid
solution.
• Homogenous distribution of coherent phases.
• Micro structurally unique – precipitates remain coherent – extensive
aging.
• Extensive aging (>190˚c) – icosahedral grain boundary precipitates.
• Precipitates & PFZs near grain boundaries – fracture process.

21. Al-Li alloys
• Low ductility & toughness – inhomogeneous nature of slip – δ’ precipitate
hardening
• Presence of δ (AlLi) at grain boundaries and PFZs – strain localization –
intergranular failure.
• Remedy :- Introducing dispersoids (Mg & Zr) & incoherent precipitates
[(Al 2 CuLi), (Al 2 Cu), or (Al 2 LiMg)]

22. Limitations ofAl-Li alloys
• Low ductility and toughness
• Cracking along grain boundaries

23. Al-Li-X alloys
• Objective – improve ductility & toughness of Al-Li alloy
maintaining high strength.
• X – Cu, Mg, Zr
• Cu & Mg – solid solution and precipitation strengthening
& minimizes PFZs
• Zr – forms cubic Al3Zr incoherent dispersoid – stable
structure
• Mg – reduction in solubility of Li in Al.

24. Al-Li-X alloys -Advantages
• 7 to 12 % higher stiffness than high strength Al alloys.
• Improved toughness – cryogenic temp.
• Fatigue crack rate – orientation – crack plane & growth direction(L-T &
T-L)

25. Al-Li-X alloys - Disadvantages
• Fatigue crack rate – orientation – crack plane & growth direction(L-T & T-L)

26. • Comparison of creep crack growth rates for aluminum-lithium alloy extrusions with those for
other aluminum alloys. Alloy 8090 contains 2.5% Li, 1.5% Cu, 1.0% Mg, 0.12% Zr, and a
balance of aluminum.

27. Thermomechanical effects
• Deformation prior to aging - increased strength and
toughness, affects precipitation strengthening.
• Example:- 2090 Al-Li alloy - (Al2CuLi) strengthening
precipitates – large coherency strain
• Nucleation on dislocations – minimize it.
• Alloys – Mg, Cr, Zr etc. – control grain microstructure
during thermomechanical treatment.

28. DifferentAl-Li alloys

30. Manufacturing
• Ingot Metallurgy.
• Rapid Solidification Metallurgy Technique

31. Applications
• Aircraft - leading & trailing edges, seat tracks & wing skins, center
fuselage.
• Space application - rockets and satellite systems, cryogenic tankage etc.

32. • Use of aluminum-lithium alloys in a commercial
aircraft