Investigation of the welding parameter dependent microstructure and mechanical properties of friction stir welded pure copper

The process window for friction stir welding of commercially pure copper was obtained, which included a welding speed ranged from 200 to 800 mm/min, a rotation speed ranged from 400 to 1200 rpm and an applied load ranged from 1000 to 1500 kg. In the stir zone, a remarkably refined microstructure with average grain size of 3.8 μm can be obtained by increasing the applied load to 1500 kg. In addition, higher applied load can promote the formation of dislocation cells, while annealing twins and dislocation entanglements are easy to form under lower applied load. The mechanical properties of the joints can be improved further by increasing the applied load, rather than only decreasing the rotation speed at lower applied load. The mechanism of the mechanical property changes in the copper joints were put forward and clarified from the viewpoint of microstructural evolution.