Effect of peening treatment for out-of-plane fatigue test on A7075-T651 alloy

To investigate the effect of peening treatment on fatigue properties, laser peening (LP) treatment and shot peening (SP) treatment were applied to an A7075-T651 aluminum alloy, and high-cycle plane-bending fatigue tests were conducted with a stress ratio of R = 0. Typical peening effects, including the surface roughness value, residual stress distribution, hardness distribution, and half-value breadth distribution, were measured. As a result, it was found that the LP treatment significantly improved fatigue life but that the SP treatment only slightly improved fatigue life. Because the negative peening effects due to a combination of the notch effect from the larger surface roughness and the embrittlement of the microstructure from strain hardening are greater than the positive peening effect of the compressive residual stress, the SP treatment decreased crack initiation life and fatigue crack propagation life. However, the LP-treated specimen had larger residual stress and deeper zero residual stress crossing the distance from the surface, both of which can improve fatigue life.