Experimental Study on Laser Shock Peening of AZ31B Magnesium Alloy Sheet

Typical specimens of AZ31B Magnesium alloy were processed by single point and continuous laser shock peening (LSP). The selected laser energy was 25 J, spot diameter was 8 mm, peening spacing was 8 mm and peening times were 2. The obtained value of residual compressive stresses were -144.3 MPa and -230 MPa for single and continuous LSP respectively, and the magnitude of residual stress was in direct proportion to the depth of deformation in definite micro-deformation range. The average surface micro-hardness in the laser spot zone was 92.42 HV, which increased by 26% as compared to 73.2 HV of substrate, the depth of hardened layer was about 0.3 mm, and the maximum micro-hardness was about 109.86 HV beneath surface of 0.05-0.075 mm. Large amount of crystal chunks appeared at the crystal grain boundaries and inside the grains, and the average grain size decreased from the untreated 7 mu m to the peened 4 mu m. The results show that the nucleation of fatigue crack can be retarded and the mechanical properties of AZ31B magnesium alloy sheet can be improved greatly with LSP process.