An investigation on the fatigue behavior of additively manufactured laser shock peened AlSi7Mg alloy surfaces

In the recent years, laser powder bed fusion of aluminum alloys has attracted extensive attention due to their capacious application in the biomedical, aerospace, and other industrial sectors. This is due to the combined capabilities of the laser powder bed fusion process and aluminum alloys bringing about complex shapes with high performance associated with light-weight design. Despite their high potential, parts produced by laser powder bed fusion suffer from residual stresses, surface irregularities and sub-surface defects limiting their full exploitation in fatigue sensitive applications. Consequently, post-processing methods such as laser shock peening can be employed to countermeasure these short-comings. This article reports on the effect of laser shock peening on the fatigue life of AlSi7Mg alloy fabricated via laser powder bed fusion. Laser shock peening induced a substantial improvement (around 50%) in the fatigue life when compared to the as-built parts. The improvements were attributed to the closure of surface and sub-surface pores, re-entrant surface features and in particular, induced compressive residual stress profile. The effects of laser shock peening were investigated through systematic multi-scale analysis through destructive and non-destructive methods. Furthermore, a simple fracture mechanics model was utilized to elucidate the effect of induced compressive residual stresses as the principal actor in the corresponding fatigue life improvement.