Effect of welding speed on metallurgical and mechanical behavior of friction stir welded pure copper

In this research, the 5-mm-thick copper plates were friction stir welded at a constant rotation rate of 600rpm with various welding speeds. Optical microscopy, tensile and microhardness test were used to study of microstructure and mechanical properties of the joints. The results show that by increasing the welding speed, the grain size nugget zone first decreased and then increased. The average hardness of nugget zone increased first and then decreased. The ultimate tensile strength and elongation of the joints decreased with increasing the welding speed due to decreasing the material plastic deformation during welding process and formation of cavity defects in nugget zone. The defect free joints were produced at lower welding speeds, and the fracture locations were in base metal. With increasing the welding speed, the fracture locations were in nugget zone.