Joining of Commercial Pure Copper via Self-reacting Friction Stir Welding

Three mm thick plates of commercial pure copper were welded via friction stir welding method using a floating bobbin tool. The effect of different process variables such as the tool transverse speed and the tool rotation speed were examined in order to create a weld with the desired properties. A defect-free weld was obtained at a rotation speed of 1400 rpm and a transverse speed of 18 mm/min with a shoulder pinching gap of 2.7 mm. After the welding process, the soundness of the welds was confirmed by non-destructive methods of visual inspection and X-ray radiography. The results of the transverse tensile test showed that the as-weld joint efficiency was 86.4%, which was higher than the joint efficiency made by the fusion welding method. The strength of the welds was such that the fracture of the workpiece was in the heat affected zone after the tensile test. On the other hand, the grain size of the weld was significantly less than the base metal. The lowest hardness around 40VHN was attributed to the middle of the thickness of the weld, while the highest hardness was in the vicinity of the lower shoulder of the tool, which was about 80 VHN.