Effective femtosecond laser shock peening on a Mg–3Gd alloy at low pulse energy 430 µJ of 1 kHz

Abstract In this paper, microstructure evolution and hardness of Mg-3Gd alloy treated by femtosecond (fs) laser shock peening (LSP) with direct and confined ablation modes were investigated in detail. Under a relatively low pulse energy of 430 µJ with a repetition of 1 kHz, the surface hardness of sample has been enhanced by 70% effectively. Compared with ns-LSP with pulse fluence of 71.7 J/cm 2 , fs-LSP with pulse fluence of 34.2 J/cm 2 is superior in the hardness increment, both of which are in the same order of magnitude. A distinct grain refinement of surface layer has been discovered and results in the increase of hardness. Nonuse of absorption and confining layers and the employment of the industry commercial fs laser with high repetition can inspire big potential LSP application in special metal material.