Effects of heat treatment process on stress corrosion cracking and microstructures of 7A05 Al alloy plate

In order to improve the stress corrosion cracking (SCC) resistance of 7A05 Al alloy, four different heat treatment processes were performed. After the heat treatments, the stress corrosion cracking resistance, mechanical properties and microstructures of 7A05 Al alloys were studied. The results show that the retrogression and reaging (RRA) treated specimens possess the highest SCC resistance with slightly reduced strength as compared with the other specimens. Thus RRA is the best process in terms of the optimal combination of SCC resistance and strength. Further TEM observation reveals that the RRA treated specimens are characterized by the fine equiaxed grains, dispersed second phase and wide precipitate free zone (PFZ). The pre-aging treated specimens show lower SCC resistance but higher strength as compared with the RRA treated ones. Equiaxed grains are also observed in the pre-aging treated samples by TEM, indicating that the anisotropy is eliminated. However, the dual aging and deformation plus aging treated specimens are demonstrated by large anisotropy.