OXIDATION OF ALUMINUM LITHIUM ALLOYS IN THE SOLID AND LIQUID STATES

Lithium additions increase the oxidation rate of aluminium alloys in the solid and liquid states. At elevated temperatures in the solid state lithium diffuses rapidly through the aluminium alloy and through oxidised surfaces to become oxidised preferentially at the oxide/air interface where it forms non-protective oxidation products. The consequent lithium depletion causes changes in the near surface microstructure and hardness to depths of up to 800 jim depending on the temperature and exposure times. Depleted surface layers can lead to substantial reductions in the strength of thin sections. Procedures for minimising oxidation and lithium depletion during processing of Al-Li alloys are discussed. Oxidation in the liquid state is important in casting, in fusion welding, and in rapid solidification processing. The behaviour of Al-Li alloys under these conditions is described. © 1990 Maney Publishing.