Effect of processing parameters on microstructure and mechanical properties of pure copper joints made by friction stir welding

The main objective of this investigation was to apply friction stir welding(FSW) for joining of pure copper plate which is 3 mm thick. Defect free welds were obtained at a constant rotation speed of 800 r/min and travel speed ranging from 60 mm/min to 300 mm/min. The influence of welding parameters on the microstructure and mechanical properties of the pure copper joints were investigated. The joints exhibit four distinct zones, parent material, heat affect zone, thermo-mechanically affected zone, and stir zone respectively. Microstructure of the stir zone consists of fine equiaxed grains due to dynamic recrystallization, the average grain size of the stir decreased with the increasing of welding speed. Microhardness distribution curve showed a"U" shape, and the hardness of the stir zone was lower than that of the parent material. The tensile strength and elongation of the joints reached about 285 MPa and 21.7% at a travel speed of 100 mm/min, which were 93.8% and 79.2% of the parent material, respectively. SEM indicated that the joint formed at the 300 mm/min failed in a brittle fracture manner and joints formed with other parameters failed in a ductile fracture manner.