Study On The Technology And Weld Properties Of 6061 Aluminum Alloy Simultaneous Double-sided Friction Stir Welding

6061 aluminum alloy is widely used in transportation,aerospace and other fields because of its low density,good corrosion resistance and good ductility.But the welding performance of 6061 aluminum alloy is poor,and the traditional fusion welding method is difficult to meet the welding requirements.Friction stir welding is a new welding technique for solid welding,which has many advantages compared with fusion welding.At present,the traditional friction stir welding still has some problems,such as large welding deformation,low welding efficiency and higher requirements for tooling equipment.Simultaneous doublesided FSW(SDS-FSW)controls the welding tools separately through both axes.The combined effect of SDS-FSW enables more uniform plate deformation,minimizes welding deformation and improves welding efficiency.The lower shaft shoulder is located below the plate to play a supporting role,so that the welding does not need the bottom plate,reducing the rigidity requirements of tooling and equipment.In this paper,the effects of SDS-FSW process parameters on the microstructure,mechanical properties and welding deformation of 8mm thick 6061-T6 aluminum alloy plate were investigated.The microstructure,joint formation mechanism,fracture characteristics and welding deformation under optimized welding parameters were studied.The microstructure,mechanical properties and residual stress distribution of SDS-FSW and Double-sided FSW(DSFSW)were compared.The main research contents and conclusions are as follows:(1)Study on DS-FSW welding parameters of 6061-T6 Aluminum alloy.Based on SDS-FSW equipment,the microstructure,mechanical properties and welding deformation of SDS-FSW at different rotation speed,welding speed and press amount were researched,and the optimal welding parameters combination was obtained.The results showed that the welding parameters had significant effects on the microstructure,mechanical properties and welding deformation of the joint.when the welding parameters are not selected properly,the joint line remnant and incomplete weld flaw of the joint have significant effects on the fracture mode and mechanical properties of the joint.(2)Study on DS-FSW micro structure,joint forming mechanism,fracture characteristics and welding deformation of 6061-T6 Aluminum alloy.Based on optimization welding parameters combination of 6061-T6 aluminum alloy,the microstructure evolution of SDS-FSW joints in different regions were studied The material flow behavior in the welding process was explored.The tensile and bending test fracture characteristics of the joint were obtained,and the deformation distributions perpendicular to and along the weld were determined.The results show that the grain size of each region had no obvious change on both sides.The fracture morphology of the optimized welding parameters is similar to that of the base metal,while stratification occurs under other parameters.The deformation perpendicular to the direction of the weld presented symmetrical distribution.The deformation is minimum in the steady state stage.The deformation of the advancing side along the direction was lower than that of the retreating side.(3)Study on microstructure,mechanical properties and residual stress distribution of SDS-FSW and DS-FSW joint.Based on optimized welding parameters,DS-FSW tests were carried out,and the differences in microstructure and mechanical properties of SDS-FSW and DS-FSW joints were analyzed.The longitudinal welding deformation and residual stress distribution of joints were investigated.The results show that the peak value of longitudinal residual stress occurs near the shoulder edge of the mixing head.Compared with DS-FSW,SDSFSW exhibited greater longitudinal residual compressive stress and lower welding deformation.