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SUMMARY INTRODUCTIONA historical perspective on the development of AI-Li alloys was given by Balmuth and Schmidt at the recent International Aluminum-Lithium Conference and is included in the proceedings published by The Metallurgical Society of AIME.l The development of AI-base alloys containing lithium began in Germany in the 1920s and was primarily concerned with additions of small amounts of lithium to age-hardening alloys to increase their strength. In the 1950s metallurgists at Alcoa recognized that lithium increased the elastic modulus of aluminum and they developed the high strength AI-Cu-Li alloy 2020. However, this alloy had low ductility and fracture toughness in the maximum strength temper. These limitations, as well as production problems, led to its withdrawal as a commercial alloy in 1969.Since 1973, the rapid escalation of fuel costs has accelerated research on developing more fuel-efficient aircraft and, consequently, on developing new Al-Li alloys, for one way to achieve more fuel-efficient aircraft is to reduce weight. Recent studies by Lewis and coworkers 2 have shown that this is most effectively accomplished by reducing the density and increasing the specific modulus and strength of the materials used for airframe components. Since aluminum alloys comprise 80 wt. % of the airframe, metallurgists are actively pursuing ways to effect such improvements in these critical materials. Besides beryllium, which has associated manufacturing and health related problems, lithium is the only known metal which improves both modulus and density when alloyed with aluminum. Each weight percent lithium added to an aluminum alloy reduces the density approximately 3% and increases the elastic modulus approximately 6%3 for lithium additions up to 4%.

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