FACTORS INFLUENCING THE ENVIRONMENTAL BEHAVIOUR OF ALUMINIUM-LITHIUM ALLOYS

Abstract
This paper discusses the microstructural features of aluminium-lithium alloys that influence their corrosion and stress corrosion behaviour. Emphasis has been given to the effect of microstructure on stress corrosion crack initiation and propagation in Al-Li-Cu-Mg-Zr alloys (e.g. 8090 and 8091). In particular, the use of both isothermal and duplex ageing routes to develop overaged microstructures with increased resistance to stress corrosion crack initiation has been assessed and significantly, crack propagation plateau velocities of both under and peak aged 8090 were found to compare favourably with both 2024-T3 and 7075-T651. The applicability of accepted test methods developed for conventional medium and high strength aluminium alloys for determining exfoliation resistance of Al-Li-Cu-Mg-Zr alloys has been evaluated and results have been obtained which illustrate the hazards of relying on visual ratings to compare exfoliation performance. Underaged tempers of Al-Li-Cu-Mg-Zr alloys exhibit greatest resistance to both exfoliation and intergranular corrosion attack.