Influence of ultrasonic rolling on surface integrity and corrosion fatigue behavior of 7B50-T7751 aluminum alloy

The surface integrity and corrosion fatigue (CF) performance of the 7B50-T7751 aluminum alloy treated by one (UR1), three (UR3), and six passes (UR6) of ultrasonic surface rolling process (USRP) were investigated in this paper. The results revealed that a modified surface layer with refined microstructure and increased microhardness was formed after the USRP, and a compressive residual stress (CRS) was induced. The CF life of all USRP-treated samples was improved, especially the life of the UR1 sample with an optimal surface integrity. The synergistic effect of surface layer microstructure refinement and CRS effectively have inhibited the occurrence and development of pitting and intergranular corrosion, prevented the initiation of CF cracks at the surface, thus led to the movement of the fatigue crack nucleation site toward the subsurface. Overall, the CRS has played a major critical role. The severe surface damage in the modified layer of the UR6 sample resulted in a partial relaxation of the CRS, in favor of secondary fatigue crack initiation, therefore when using the USRP treatment to improve the CF life of the 7B50 aluminum alloy, the effect of surface integrity should be fully considered.