Effect of quenching residual stress on precipitation behaviour of 7085 aluminium alloy

Abstract

The quenching-induced residual stress in ultrahigh strength Al-Zn-Mg-Cu alloys has a great influence on their precipitation behaviour in subsequent heat treatment and the properties of the final products. In the present work, the cladding quenching method was employed for 7085 Al alloy slabs to tailor different quenching residual stresses. Then the effects of quenching residual stress on the precipitation behaviour of the 7085 Al alloy were investigated through finite element analysis, residual stress and hardness distribution measurements and microstructural examinations. The results indicate that the reduction in residual stress increases with increasing cladding layer thickness. For a cladding layer thickness in the range of 1-1.4 mm, the residual stress is almost eliminated. The hardness at the surface of the aged sample with a large compressive residual stress is decreased, while the hardness at the centre of the sample with a large tensile residual stress is increased. The hardness is approximately identical between the aged samples with little or no residual stress. The elastic lattice distortion caused by residual stress is found to promote the nucleation of precipitates during the artificial ageing process. The in-depth mechanisms for the effect of quenching residual stress on the precipitation of 7085 Al alloy are also discussed.