Research On The Fatigue Behavior Of Magnesium Alloy Treated By Laser Shot Peening Based On Numerical Analysis And Experiment

Laser shot peening(LSP) is a new surface strengthening technology which uses high-energy pulse laser to create a high amplitude shock wave.The strengthening mechanism is similar to traditional strengthing technology,and the strengthening degree is mainly depends on the distribution of residual stress field.In this paper,Combined with numerical simulation and experiment,magnesium alloy treated by LSP is studied and the test results are also statistically analyzed.The main contents are shown as following:The forming mechanism of residual stress induced by LSP is studied and the influence mechanism of residual stress on the fatigue performance is explained by internal fatigue limits theory reasonably.On the basis of the above analysis,compressive residual stress field intensity(S) is introduced to estimate the effect of compressive residual stress field on fatigue performance.Based on ABAQUS and MSC.Fatigue software,a finite element analytical model for predicting the fatigue life of magnesium alloy treated by LSP is established.The fatigue life of magnesium alloy specimen with center hole before and after LSP is predicted using Box-Behnken experimental design.The simulation results indicated,the change trends of fatigue life is similar to that of compressive residual stress field intensity with the variation of level of the laser parameters.But the fatigue crack source will appear at the tensile stress zone in the edge of peening areas when the parameter level is too high.The effect of laser processing parameters(peak pressure of shock wave,spot diameter and peening number) on the compressive residual stress field intensity, deforming depth and fatigue life are analyzed.Quadratic regression predicting model for fatigue life is established,and the rationality of model is verified.Finally,the optimal combination of laser process parameters oriented to anti-fatigue manufacture is optimized. Statistical analysis results show that the fatigue life will increase with the larger of compressive residual stress field intensity,and reduce while increasing the surface deforming depth to a certain extent.The compressive residual stress,surface morphology and roughness,micro-hardness of material as well as microstructure before and after LSP are tested and compared.The fatigue tensile test of light-weight magnesium alloy by LSP is carried out preliminary,and then the whole fatigue life is tested.At the same time,the macro- and micro- morphology of fatigue fracture are analyzed.The results show that appropriate parameters are benefit for the improvement of the fatigue life of magnesium alloy.