Dissimilar Metal Joining of Pure Copper and Al 6061 by Using Friction Stir Spot Welding

Abstract

Dissimilar metal joints with good electrical conductivity and high mechanical strength are generally required in electrical industry. In this work joining of Al 6061 and pure copper sheets by FSSW process was studied. Friction stir spot welding (FSSW) is a solid-state welding technology; it is energy efficient, environment friendly and versatile. FSSW is derived from Friction-Stir Welding (FSW). FSSW process is proving to be a better alternative to Resistance Spot Welding (RSW). In this work feasibility of joining Al 6061 and pure copper sheets by FSSW process was studied using a cylindrical pin tool. Tool rotation speed, plunge depth and dwell time were varied to determine the optimum process parameter so as to achieve high values of lap shear separation force and cross tension force. For process parameters optimization Taguchi technique based on L16 orthogonal array was used. Joints were made by altering the top-bottom position of copper and aluminium alloy sheets. For joints with pure copper top-AI 6061 bottom, the optimum values for processing parameters were 1600 rpm rotational speed, 1.9 mm plunge depth and 8 sec dwell time. For joints with Al 6061 top -pure copper bottom the optimum values were 1200 rpm rotational speed, 1.9 mm plunge depth and 12 sec dwell time. Their respective lap sheet forces were 4638N and 4235 N. Nugget pullout failure was observed in either type of joints. The electrical resistivity for copper-top joints was in the range of 0.15x10 -4 Ω-m to 0.30x10 -4 Ω-m and for copper-bottom joints, it was changing from 0.25x10 -4 Ω-m to 0.45x10 -4 Ω-m.