Investigation of temperature distribution, microstructure evolution, and weld performance in stir friction welded joints of 6061 aluminum alloys

In this study, we consider the use of the finite difference heat dissipation model, plastic deformation material control continuity equation, and Johnson–Cook model for numerical analysis of friction stir welding (FSW) under different welding parameter conditions and experimental investigation in terms of microstructure and macroscopic mechanical properties. Compared with the traditional thermal analysis model, the model considers the mutual coupling of the heat field and flow field in the welding process, and the analysis results are more accurate. The temperature history of the FSW process with plastic flow rate for different welding parameters is considered. On this basis, the effects of different spindle speeds and welding traveling speeds on the welded joints, as well as the impact of varying mesh size dimensions on the convergence of the model and the reduction of the solution time, were investigated. The validity of the coupled model is verified by comparing the numerical welding temperatures with the experimental results. The results show that the error between the numerical analysis results and the observed temperature results is only 2%, and the main reason is that the actual stirring needle absorbs part of the heat when it passes through the temperature measurement point, resulting in the peak temperature of its corresponding point does not appear. Under the conditions of different welding parameters, the mechanical properties showed a rising and then decreasing trend with the temperature increase due to the change of microstructure affected by heat. The optimum welded joint was obtained at 1100 rpm.