Effect of dynamic recrystallization on microstructure and properties of multilayer Al foils friction stir welding

In this study, friction stir welding (FSW) was used to weld multi-layer Al foil and Al plate, and the defect-free welded joint was successfully obtained. In the stirring zone (SZ), due to the extrusion of the shoulder and the rotation of the stirring pin, the original layered structure of SZ is destroyed, and the original grains are destroyed and dynamically recrystalized to form fine equiaxed grains. With the decrease of welding speed, the heat input increases, the dynamic recrystallization degree (DRX) of SZ increases, the proportion of low angle grain boundaries (LAGBs) increases from 20.5% to 45.0%, and the grain size of SZ decreases from 1.53 to 0.93 μm, which affects the performance of the joint. The hardness of each welding parameter SZ is higher than that of the base material. With the increasing degree of DRX, the hardness of SZ continues to rise, and the electrical conductivity decreases from 57.5% international annealing copper standard (IACS) to 52.5%-56.2% IACS. The tensile strength of the joint reaches its maximum first and then decreases with the increase of DRX.