Stress corrosion cracking behaviour of 8090 Al–Li alloy in a chloride containing medium

Studies of the stress corrosion cracking behaviour of an Al–Li alloy (8090) in the underaged, peak aged and overaged conditions were conducted using a constant load technique in a chloride containing solution. The stress corrosion tests were carried out using a range of applied stress values under both anodic and cathodic polarisation. It was observed that the material is susceptible to stress corrosion cracking in all aged conditions. However, the peak aged alloy displayed the lowest resistance to stress corrosion cracking, while the underaged material had the greatest resistance to stress corrosion cracking among the three conditions studied. The presence of δ precipitates throughout the matrix of the peak aged material imparts constraint to plastic deformation, making it more susceptible to stress corrosion cracking when compared to materials in the underaged or overaged conditions. Study of the effect of polarisation on the stress corrosion response of the material has revealed that no cracking occurs when the material is cathodically polarised, while anodic polarisation accelerates the stress corrosion cracking. Initial stress corrosion crack propagation occurs intergranularly, but final failure is transgranular. It has been noted that the initiation of stress corrosion cracking is associated with the dissolution of grain boundary precipitates. However, hydrogen induced localised plasticity may contribute at a later stage to the propagation of cracks.