Surface characteristics and stress corrosion behavior of AA 7075-T6 aluminum alloys after different shot peening processes

Shot peening is often reported as being beneficial to stress corrosion cracking resistance; however, the increased surface roughness induced by shot peening may promote localized corrosion pitting. Here, AA 7075-T6 aluminum alloys were treated by different shot peening processes, and the surface characteristic, including refined microstructure, residual stress and surface roughness, were characterized, then its effect on localized corrosion pitting and stress crack propagation behavior were investigated. Compared with single shot peening, the microstructure refinement was not further enhanced by dual shot peening with adding a subsequent low intensity of micro-shot peening. The surface residual stress distribution become more uniform, and the average surface residual stress value was increased from −158 MPa to −175 MPa. The maximum residual stress was synchronously increased from −302 MPa to −319 MPa. Meanwhile, the surface roughness (Ra) value was decreased from 4.05 μm to 2.05 μm. Compared with single shot peening, the degree of surface localized corrosion pitting was alleviated after dual shot peening due to its low surface roughness and more uniform compressive residual stress distribution. The depth of stress corrosion cracking for dual shot peening was decreased with a minimum value of 33 μm, which may be ascribed to the high maximum compressive residual stress at the subsurface.