Material behaviour characterization of Friction Stir Spot Welding of Copper

Friction stir spot welding (FSSW) is considered as a replacement technology of conventional resistance spot welding for manufacturing lighter vehicles in the automotive industry. FSSW technique was applied to join pure copper for industrial uses. The welding was conducted on an Intelligent Stir Welding for Industry and Research (I-STIR) Process Development System (PDS). Rotational speeds of 1200, 1600 and 2000 rpm were employed. The spot welds were characterised through the evolving microstructure, microhardness, tensile and the fracture surfaces. The microhardness measurements were conducted using the Vickers microhardness indenter and the tensile shear test was used to determine the mechanical properties of the welds. Optical microscope and scanning electron microscopy technique (SEM) were used for the microstructure analysis while the Energy Dispersive X-ray spectroscopy (EDS) was used to analyse the debris observed in the specimens after welding. It was found that the microhardness profiles of the processed samples revealed a decrease in the hardness value at the joint interface of the weld, this results in the lower strength of the welds, this is attributed to the heat and the stirring process generated during the processing due to a large stir zone. The process was evaluated in order to make it an alternative welding technique and to produce a material with high strength for industrial application. Microstructure evolution and the mechanical characterization techniques were employed to evaluate the properties of the welded materials. It was deduced that the rotational speeds employed influenced the evolving properties of the welded specimens.