Influence of the tool rotational speed on the microstructure and joint strength of friction-stir spot-welded pure copper

Copper is very difficult to be spot welded with conventional fusion-welding techniques due to a high thermal diffusivity. Friction-stir spot welding (FSSW) is a novel solid-state welding process, suitable and effective for spot welding copper. Commercially pure copper sheets of 3 mm thickness were spot welded using an industrial friction-stir welding machine. The spot welds were made by varying the tool rotational speed at three levels. The spot welds were characterized using light microscopy. The shear-fracture load was evaluated using a computerized tensile-testing machine. The results revealed that the tool rotational speed remarkably influenced the microstructure, the shear-fracture load and the mode of fracture. Keywords: copper,