Microstructure and Mechanical Properties of Friction Stir Welded Pure Copper

Conventional welding of copper and its alloys tends to degrade the mechanical strength at the welded area due to high thermal diffusivity and melting point. Friction stir welding (FSW) is an excellent alternative for joining of these materials against fusion joining. FSW is an emerging solid state joining process in which the material that is being welded does not melt and recast. This process uses a non-consumable tool to generate frictional heat in the abutting surfaces. The main objective of this investigation is to use FSW for joining of 3 mm thick copper sheet using taper cylindrical tool pin profile. The defect free welds were obtained at a tool rotational speed of 900rpm and 1120 rpm and traverse speeds of 25, 31.5, 40 and 50 mm/min respectively. Mechanical and microstructure analysis has been performed to evaluate the characteristics of friction stir welded copper. From the investigation it is found that the joints fabricated at a tool rotation speed of 900 rpm and traverse speed of 40mm/min resulted in better mechanical properties compared to other tool rotation and traverse speeds. The tensile properties of all the weld joints showed a relative correspondence to the variation of the hardness in the weld zone. The observed results were correlated with the microstructure and fracture features.