Simulation Analysis Of Residual Stress For 6061 Aluminum Alloy Friction Stir Welding

Friction stir welding is widely used in the welding of light metals such as aluminum alloy.Friction stir welding has the advantages of high strength and small welding deformation.However,the welding process of friction stir welding is a complex process which is coupled with temperature change,stress,strain and metal flow.At present,the process of friction stir welding is mostly simulated by the finite element method.The research usually adopts the quasi-static method of loading a simplified moving heat source and the dynamic method of only simulating the stable welding stage,but the research of the whole welding process and optimization of process parameters are rarely reported.Therefore,this paper uses finite element software named ABAQUS,using the thermal-solid coupling method and the thermal-fluid-solid coupling method,treats 6061 aluminum alloy welded plate as solid and fluid to simulate friction stir welding whole process(five stages of preheating,pressing,processing,unloading and cooling),the temperature field and stress of the welding plate and the distribution of residual stress after welding in each stage of the welding process are obtained.The error between the residual stress obtained by finite element simulation and the residual stress experimental measurement by X-ray diffractometer is small,the accuracy of the model is verified.With the smaller comprehensive residual stress after welding as the optimization goal,the orthogonal experimental optimization method is used to optimize the welding process parameters(the speed of the stirring head,the traveling speed of the stirring head,the pressing amount of the stirring head and the shoulder radius of the stirring head),and the optimal combination of welding process parameters was obtained.The research results show that:(1)the distribution of the temperature field and residual stress obtained by the thermal-solid coupling method and the thermal-fluid-solid coupling method are relatively close,with only a slight difference in numerical values;(2)Compared the results obtained by the two finite element methods with the experimental measurement results,the error of the thermo-fluid-solid coupling method is smaller,which proves that the thermo-fluid-solid coupling method is superior to the thermo-solid coupling method;(3)the welding temperature in the processing stage is about 315℃,respectively and 325℃,in the vertical weld direction,the peak values of the longitudinal residual stress after welding appear at the edge of the weld area,and the AS zone is greater than the RS zone.The longitudinal residual stress after welding are about 85 MPa and 63 MPa respectively,the errors with the experimental measurement results are 21.68% and 7.81%,respectively,and the transverse residual stress after welding are about-20 MPa and-16 MPa,respectively,and the errors with the experimental measurement results are 17.12% and 10.88% respectively;(4)The optimal combination of welding process parameters is the rotation speed of 2500r/min,the travel speed of 500mm/min,the pressing amount is 0.25 mm and the shoulder radius is 5mm,the comprehensive longitudinal residual stress after optimization is reduced by 29.2% compared with that before optimization.The certain reference for the temperature field and stress simulation of the welding plate during the friction stir welding process and the residual stress simulation after welding is provided by the research results of this paper,and the certain theoretical basis for the optimization of welding process parameters is provided.