Effects of laser peening treatment on high cycle fatigue properties of degassing-processed cast aluminum alloy

It is well known that the degassing (DG) process is very useful for reducing cast defects such as porosities, micro-shrinkages, and inclusions in metallic alloy casting processes. The authors had previously clarified that DG processing is an effective method for improving the fatigue property of cast aluminum alloy. In this study, a treatment involving laser peening without coating (LPwC) was applied to the DG process cast aluminum alloy with an aim to further improve the fatigue property of the alloy. Fatigue tests under rotating bending were carried out on the LPwC-treated DG process cast aluminum alloy in order to investigate the effects of the LPwC treatment on fatigue properties such as fatigue strength, crack initiation, and propagation behavior. From the results, it was found that the fatigue life and fatigue strength at 10^7 cycles of the DG process cast aluminum alloy improved by the LPwC treatment. The possible reason for this improvement is the deceleration of the surface crack growth rate due to the compressive residual stress in the surface layer induced by the LPwC treatment.