Improving the fatigue limit of FSW6061 Al alloy welded joints by surface spinning rolling

To optimize the fatigue performance of the friction stir welded (FSW) 6061 Al alloy welded joint, a surface spinning rolling (SR) strengthening process has been employed in this study. Compared to a typical shot-peening (SP) process, a gradient-hardened microstructure with larger thickness and a deeper residual compressive stress layer was introduced. Furthermore, a lower surface roughness was also achieved after the SR strengthening treatment. These factors are beneficial for effectively suppressing the fatigue crack initiation for 6061 Al alloy welded joints. Consequently, the fatigue test results show that after the surface treatment, the fatigue limit of the welded joint increases from 145 MPa in the welded state to 167 MPa in the strengthened state, successfully raising the fatigue limit of the welded joint to the same level as the matrix. In contrast, SP treatment failed to improve the fatigue limit of the welded joint, possibly because of the high surface roughness. This work guides the fatigue resistance design of Al alloy weld plates.