Effect of the tool rotation direction on the joint properties of the pinless friction stir spot welding of pure copper

Abstract

The main goal of this work is to explore the effect of the tool rotation direction with spiral groove on the joint properties of the pinless friction stir spot welding (PFSSW) of thin pure copper sheet. For this purpose, the surface appearance, cross-sectional morphology, microhardness, welding temperature and joint strength of the welded joints under the tool rotation conditions of clockwise and anticlockwise were studied comparatively at different rotation speeds. The fracture modes of welded joints under different tool rotation directions were also analyzed. The results show that the tool clockwise rotation has higher welding strength than anticlockwise rotation at lower rotation speeds, while the opposite is true at higher rotation speeds. Under the clockwise rotation of the tool, the fracture modes of the welded joints are shear fracture and plug shear fracture. When the tool rotates anticlockwise, the fracture modes of the welded joints are shear fracture and plug shear-pullout fracture. Furthermore, the depth of the stir zone produced by anticlockwise rotation of the tool is higher than that produced by clockwise rotation. Overall, the microhardness with anticlockwise rotation of the tool is higher than that with clockwise rotation. In addition, the tool rotation direction has little effect on the welding temperature. The research content can provide a reference for the selection of the tool rotation direction of the PFSSW.