Experimental Studies And Numerical Simulation On Laser Induced Shockwave In AZ31B Magnesium Alloy

Laser shock processing (LSP) is a new surface hardening technology. It has been widely used for the research of material's surface modification. Magnesium alloy is an important material in aerospace, automotive etc. So it is meaningful to study LSP on magnesium alloy. This study can be helpful to improve the property and fatigue life of magnesium alloy.In the present work, based on the mechanism of LSP, the induced Shockwave during LSP and the generation of residual stress was discussed. The finite element model was used to study the attenuation law of the peak pressure of stress wave, and the results were compared with the experimental results. Also, the effect of overlay and laser power density on the peak pressure of the Shockwave was studied by experimental method. The main research contents in this paper are listed as follows:The attenuation of the Shockwave in magnesium alloy was investigated by FEM (Finite Element Method) simulation and experiment. First, through describing some key problems in the model construction, the finite element models were used to simulate the attenuation of the Shockwave in the magnesium alloy, and the average propagation velocity and the peak pressure of the Shockwave were obtained. Second, the relative pressures of the shock waves were measured by PVDF gauge. The attenuation law of laser shock wave was obtained by measuring the intensity pressures on the rear surface of the target for different thickness the shock waves had passed each time. Then the experimental results were compared with the simulation results and they agree well. The results show that the average velocity of the shock wave attenuation in magnesium alloy is in good agreement with the propagation velocity of stress longitudinal wave; the law of the shock wave attenuation is exponential.In order to study the effect of overlay and laser power density on shockwave, the laser-induced Shockwave was measured by a PVDF gauge and a digital oscillograph. Based on the piezoelectric waves measured in the overlay geometry and the direct ablation regime, the pressure waves were obtained and compared; the pressure waves acquired in the different laser power density conditions were also compared and analyzed and obtained the curve about the peak pressure as a function of laser power density. The research results showed that the peak pressure of laser Shockwave in the overlay geometry was about as eight times as it was in the direct ablation regime, and the duration time of the pulse was extended obviously. Below the dielectric breakdown threshold of the transparent overlay, the peak pressure of laser Shockwave was improved with the increase of the laser power density.