New Approaches to Alloy Development in the Al-Li System

Abstract

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%.

Explosive shock and laser exposure of metallic and ceramic materials

“…Two sets of samples, one as received (extruded) and the other solution heat treated at 530°C for 1 hour and quenched, were exposed to shock pressures of one, two and three layers of Dupont Data sheet C-1; the thickness changes were assumed to correspond to a commensurate increase in the pulse duration of the shock wave [6].…”

Fatigue Crack Growth Behaviour in Friction Stir Welded Aluminium-Lithium Alloy Subjected to Biaxial Loads

“…Up to its solubility limit of 4.2% [32], each weight percentage lithium reduces the aluminium alloy density by approximately 3% and increases its elastic modulus by 5% [33]. Precipitation hardening of aluminium lithium is achieved by artificial ageing after solution heat treatment [34].…”

Microstructure and precipitation in Al–Li–Cu–Mg–(Mn, Zr) alloys

“…Lithium is the lightest metallic element, which reduces the density and increases the modulus of Al-based alloys. 2 In addition, Li can allow the precipitation strengthening of aluminium by a homogeneous distribution of coherent, spherical δ'…”