Effect of shot peening on microstructure and fatigue life of 7A12 aluminum

The effect of shot peening as mechanical surface treatment on high cycle fatigue property of the high-strength aluminum alloy 7A12 was investigated. The microstructure and fracture of the alloy before and after shot peening were analyzed using SEM and TEM. The residual stress was investigated by XRD. The results show that shot peening increases the fatigue strength by 26%. Shot peening causes residual compressive stress layer in which grain is refined and dislocation is increment. The increase of fatigue strength after shot peening is attributed to the inhibition of fine crystalline zones and dislocations on fatigue crack initiation and the prevent propagation of residual compressive stress on early fatigue crack propagation. Analysis of the fracture surface reveals that residual compressive stress and microstructure are beneficial to the reduction of the fatigue crack growth rate.