为了研究激光冲击处理对镁合金焊接件力学性能的影响，采用激光波长1064 nm，脉冲宽度15 ns，脉冲能量4 J，光斑直径3 mm的钕玻璃脉冲激光器，对AZ31B镁合金交流氩弧焊接件进行冲击处理。采用光学显微镜(OM)观测激光冲击前焊接接头微观结构，采用透射电子显微镜(TEM)和X射线衍射仪(XRD)观测激光冲击后焊接接头表层微观结构，采用扫描电子显微镜(SEM)观测试样断口，并分析了力学性能提高的机理。实验结果表明：根据优化的激光参数，能在焊接接头表层制得纳米晶，晶粒大小为35 nm左右；激光冲击处理改变了焊接件热影响区的应力状态，由残余拉应力60 MPa转变为残余压应力-125 MPa；激光冲击处理后，试样的抗拉强度提高了15.2%，屈服强度提高了15.7%，表面硬度提高了78.2%，平均冲击功提高了60%。AZ31B镁合金焊接件力学性能的提高是表面纳米化、应变硬化和残余压应力共同作用的结果。

In order to study the effect of laser shock processing (LSP) on mechanical properties of welded magnesium alloy, tungsten inert-gas (TIG) welded AZ31B magnesium alloy sheets are processed using NdYAG laser with wavelength of 1064 nm, pulse width of 15 ns, pulse energy of 4 J and spot diameter of 3 mm. The microstructures of welded joint are examined through optical microscope (OM) before LSP. The microstructures of welded joint surface layer of sample are characterized by transmisstion electron microscope (TEM) and X-ray diffractometer (XRD) after LSP, and fracture surfaces are analyzed by scanning electron microscope (SEM). The mechanism which causes the mechanical properties improvement is discussed. The results show that nanocrystalline can be produced on the surface layer of TIG welded joint by using optimized laser parameters, and nano grain size is about 35 nm. The surface residual stress of heat affected zone is converted from tensile stress (60 MPa) to compressive stress (-125 MPa) by LSP. Tensile strength and yield strength are improved by 15.2% and 15.7%, respectively, and surface micro-hardness is enhanced by 78.2%. Furthermore, the mean impact energy of samples is increased by 58.8% after LSP. The mechanical properties improvement is attributed to a combination effect of surface nanocrystallization, strain hardness and residual compressive stress.