Fatigue performance of laser shock peened Ti6Al4V and Al6061‐T6 alloys

Abstract Propagation of fatigue crack in laser shock peened metallic component is retarded by introduction of deep compressive residual stresses during the process. Apart from large compressive residual stress build‐up near the surface, surface topography is also significantly altered during laser shock peening. However, a systematic evaluation of the individual effects of residual stresses and surface topography as well as their interaction effects on fatigue crack initiation and growth is still lacking. This study investigates the effect of laser shock peening on near‐surface properties of Ti6Al4V and Al6061‐T6 alloys and how these changes dictate their overall fatigue performance. Microstructure, surface topography, hardness and residual stress state of the alloys are investigated before and after peening, and four‐point bending fatigue tests are performed to obtain Wöhler curves (S‐N curves) for each case. The results show that both surface residual stresses and surface topography influence the fatigue life of a component. Compressive residual stresses were induced to a depth beyond 1 mm for both alloys. Fatigue life of Ti6Al4V alloy increased by at least 1.28 times after laser shock peening due to the introduction of deep compressive residual stresses with minimal change in surface topography. By contrast, the improvement is nominal for Al6061‐T6 alloy due to the surface roughening effect introduced by laser peening, which results in early crack initiation and negates the beneficial effect of compressive residual stresses.