Microstructure and Mechanical Properties of Friction Stir Welded Pure Cu Plates

The process window for the friction stir welding of fully annealed commercial pure Cu was determined at an applied load of 1000kg, which includes a welding speed that ranged from 200 to 800 mm/min, and a rotation speed that ranged from 500 to 1300 rpm. In the stir zone of sound welds, a remarkably refined microstructure with the average grain size of 6.9 μm can be obtained by decreasing the rotation speed to 1000rpm. However, the grain size becomes larger than the base metal when the rotation speed is higher than 1300rpm. The stir zone may contain a structure composed of a high density dislocation cell of large developed annealing twin. The joints welded at a rotation speed less than 1300 rpm fractured in the base metal. However, the joints welded at a rotation speed higher than 1300 rpm fractured in the stir zone. The mechanism of the mechanical property changes in the Cu welds was proposed and clarified from the viewpoint of microstructural evolution