Elucidating the mechanism of defect formation in the 7050-T7451 aluminum alloy by laser shock peening

Abstract

The laser energy directly affects the strengthening of materials during laser shock peening (LSP). In this paper, the effect of propagation and attenuation shock wave on LSP was studied. Combined with the strengthening effect and defect degree, the best impact parameters and the effects of different impact pressures were obtained. The simulation and experimental results demonstrated when the unloading wave chased the shock wave and caught up at 100-200µm in the depth direction, the possibility of strengthening defects increased and the occurrence position deepened with the increase of laser energy. There was no strengthening defect on the surface of alloy when the impact pressure 4σHEL > (P) > 3.5σHEL . Strengthening defects appeared in the form of cracks 184.61µm from the surface of the alloy. When P > 4σHEL , the strengthening defects appeared on both the surface and subsurface, where the surface defects in the form of holes. The subsurface defects in the form of cracks that appeared 200µm away from the surface resulted from the unloading wave meeting the shock wave. Based on the research and the Hugoniot elastic limit, the optimal impact pressure range to demonstrate the best strengthening effects and to mitigate the formation of strengthening defects is 2σHEL < P < 3.5σHEL .