Emerging Aerospace Materials:
Aluminum-Lithium
Presented By: Joshua Katz
Presented For:
Dr. Richard Hale, AE 510: Materials and Processes
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Alloy Composition
? Composed of two very different elements.
– Figure 1 shows the element’s in the Periodic Table.
? Aluminum (Atomic Number: 13).
– Most abundant metal on the Earth.
– Transition metal.
– Heavy aerospace use due to its strength, toughness,
corrosion resistance, weight and formability.
• Table 1 summarizes the most common Al alloys used.
? Lithium (Atomic Number: 3).
– Highly reactive alkali metal.
– Typically used in spacecraft ventilation systems and
nuclear weapons (Reference 6).
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Component Elements
Figure 1: Periodic Table of Elements (Reference 5)
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Aluminum Alloys
Table 1: Common Aluminum Alloy Types (Reference 2)
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Properties
? History.
– Alloy first proposed/produced during 1950’s.
– Currently somewhat used in military aviation and
spacecraft, but no commercial aircraft use.
? Mechanical Properties.
– Most alloys are 2-3% lithium with traces of copper and
magnesium.
– Body Centered Cubic crystal structure.
– Comparison to conventional Al alloys (Reference 7):
• 10% lower density that conventional aluminum alloys.
• 10% higher modulus of elasticity
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Properties II
? Formation.
– Although Li is highly soluble in Al (5.2% max), the two
elements do not mix when naturally cooled.
– Alloy is formed by rapid quenching.
• Eutectoid Point: 7.5% Li at 875°K, shown in Figure 2.
? Refinement.
– T4 and T6 Heat Treatments.
• Anneal at 800-870°K then artificially age at 42-475°K
(Reference 9).
– Precipitate Hardening.
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Properties III
Figure 2: Aluminum-Lithium Equilibrium Diagram (Reference 8)
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Analysis
? Strengths.
– Comparison to Conventional Alloys
• 10% lower density = Reduced Weight
• 10% higher Modulus of Elasticity = Increased Strength
• Table 2 shows these in greater detail.
– Same hardness as Martensitic steel.
– Stronger than some many composites and Titanium.
– Improved fatigue life.
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Analysis II
Table 2: Strengths of Aluminum Alloys (Reference 11)
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Analysis III
? Weaknesses.
– Formation.
• Cannot be welded (heat drives lithium out of solution) or
riveted (holes cause delamination of grain boundaries).
• Expensive mfg. processes required due to volatility of Li.
• Rapid Quenching = Poor Ductility
– Corrosion.
• Radiation causes Li break down, releases hydrogen gas.
• Galvanic reactions between elements can occur.
? Result.
– Al-Li costs 3x as much as conventional Al alloys, and is
more expensive than composites and titanium.
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Industrial Uses
? Commercial Aviation.
– None.
• Removed from 777 design due to cost considerations.
– Replaced with Titanium.
? Military Aviation.
– EH101 Eurocopter structure.
– F-16 bulkheads and fuselage structure (Reference 3).
– Removed from Lockheed F-22 and JSF designs due to
cost considerations.
? Space Applications.
– Space Shuttle.
• Al-Li replacement hydrogen tank increases payload by
7500 lbs by decreasing shuttle’s weight.
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Industrial Uses II
Figure 3: Space Shuttle External
Fuel Tank (Reference 12)
Figure 4: EH101 Al-Li 8090 Support
(Reference 10)
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Conclusion and Recommendations
? Conclusions.
– Al-Li offers greater strength, lower weight and longer
fatigue life than conventional aluminum alloys, making it
ideal for Aerospace use.
– Due to the dissimilarity of the components, Al-Li is
difficult to produce and form and is so costly that it is
not widely used.
? Recommendations.
– Further Al-Li research should focus on improved
manufacturing techniques to reduce the material’s cost.
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References
1. Aluminum Now-Airplanes. Available:
http://www.aluminum.org/aluminumnow/substory.cfm?articleid=59
2. Alloys of Aluminum. Available:
http://me.mit.edu/2.01/Taxonomy/Characteristics/Aluminum/Alloys.htm
3. ASCE Construction and Materials Community. Available:
http://www.asce.org/construcmat/nae_smco.cfm
4. Kalpakjian, Seope and Schmid, Steven R. Manufacturing Engineering and Technology.
New Jersey: Prentice Hall, 2001.
5. Freedman, Roger A. and Young, Hugh D. University Physics. New York: Addison-Wesley
Publishing, 1996.
6. Microsoft Encarta Encyclopedia 1996 ed.
7. King, F. Aluminum and Its Alloys. New York: Ellis Horwood Limited, 1987.
8. Mondolfo, L.F. Aluminum Alloys. Boston: Butter Worths, 1976.
9. Hatch, John E. Aluminum: Properties and Physical Metallurgy. Ohio: American Society for Metals,
1984.
10. Kaufman, J. Gilbert. Introduction to Aluminum Alloys and Tempers. Ohio: American Society for
Metals, 2000.
11. Davis, J.R. Corrosion of Aluminum and Aluminum Alloys. Ohio: American Society for Metals, 1999.
12. National Aeronautics and Space Administration. Available: http://www.nasa.gov
13. Brown, Alan S. Al-Li Comes Back to the Future. New York: American Institute of Aeronautics and
Astronautics, 1998.
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