Abstract: A 6005A-T6 aluminum alloy sections was subjected to stationary shoulder friction stir welding.The microstructure and mechanical properties of butt-lap joints produced by stationary shoulder friction stir welding were investigated using an optical microscope,microhardness tester,electronic universal testing machine and highfrequency fatigue testing machine.The results demonstrate that the microstructure of the butt-lap joint in the stir zone was occurred dynamic recrystallization,resulting in the formation of fine equiaxed grains with an average size of approximately 5μm.In contrast,the grain size in the heat affected zone was significantly larger,reaching an average of about 100μm.The results of the hardness test indicate that the hardness of joint exhibits a“W”distribution pattern.The mean yield strength,ultimate tensile strength and elongation of the welded joints were found to be 143MPa,191MPa and 3.53%,respectively.It was observed that all the joint tensile specimens fractured in the heat affected zone.The median fatigue limit of the joint under the condition of 1×10~7 cycles is 112MPa,while the lower fatigue limit of the joint is 90MPa when the confidence level is 95% and the probability of failure is 5%.This study provides fundamental theoretical data for the application of stationary shoulder friction stir welding technology in the manufacturing of aluminum alloy car bodies.