Effect Of Surface State On Microstructure And Properties Of Aluminum Alloy FSW Welding Joints

In recent years,with the development of railway passenger cars in a direction of higher speed,convenience,and safety,the weight of trains has entered the field of vision,and aluminum alloys have attracted attention as a new generation of vehicle body materials.6082-T6 Aluminum Alloy is Al-Mg-Si Aluminum Alloy,which is a heat-treatable aluminum alloy and has excellent mechanical properties.However,welding of aluminum alloys has always had many problems,such as the formation of pores and slag during surface oxide film welding.,easy to produce hot cracks,a lot of shrinkage stress.Friction stir welding is a kind of solid phase connection technology invented by the British Welding Research Institute.It solves many problems of aluminum alloy welding effectively.This paper studies the microstructure and properties of friction stir welding joints of aluminum alloys with different surface states.Tensile,bending,microhardness,metallographic,pulsating tensile fatigue tests were used to compare the effects of different surface conditions on the performance of aluminum alloy friction stir welding joints.The tensile strength of friction stir welding joints of aluminum alloys with different surface states meets the requirements,and the joint strength coefficient is greater than 0.7.All the specimens are fractured in the heat affected zone and have good tensile properties.The state of the surface before welding had little effect on the tensile strength,but the surface state after welding was less polished and the tensile strength increased.Pre-weld and post-weld grinding,pre-weld and post-welding front grinding,pre-weld grinding and post-weld back grinding,pre-welding grinding and post-welding grinding,All face bends and back bend test specimens are qualified.so the surface state has little effect on the bending performance.The microhardness distribution of all joints was "W" type,and the surface state had little effect on the joint microhardness.All joint microstructure did not change significantly.The comparison of joint fatigue performance shows that the pre-weld grinding has a higher fatigue limit than the non-grinding pre-welding.The post-weld grinding has significantly higher fatigue limit than the non-grinding.The pre-weld grinding and reverse grinding after welding has the lowest fatigue limit.This is due to the presence of flash on the front side of the friction stir welding joint,resulting in stress concentration and thus reduced fatigue performance,which is also consistent with the results obtained by the tensile and bending tests.In summary,the state of the surface before welding has little effect on the performance of aluminum alloy friction stir welding joints.Grinding the surface after welding can improve the mechanical properties of the joint.The surface state has little effect on the joint microstructure.