ELECTRICAL AND MECHANICAL BEHAVIOURS OF FRICTION STIR BASED WELDED ALUMINIUM AND COPPER ALLOY

Abstract

Fusion weld – induced undesirable intermetallic compounds impair electrical conductivity of Al / Cu joints. Thus, there is a need to unravel the best approach of improving electrical conductivity of Al / Cu joint. This research focuses on the application of friction stir clinching approach in improving the electrical and mechanical performance of Al/Cu joints for electrical applications. Friction stir clinching process was performed on 3mm thick Cu and Al alloys. Overlapped Al/Cu joints were produced on a vertical milling machine based on the designed L9 orthogonal array of Taguchi method. Tool rotational speed, dwell time, and plunge depth were varied. K- thermocouple was used to take the in-situ temperature history of the welds during the joining process. Welding process was modeled and simulated using an ANSYS simulation package in order to further understand the welding mechanism. The microstructure and fracture surface of the joints were viewed under optical microstructure (OM) and scanning electron microscope (SEM). The electrical resistivity of the joint was also identified via a designed electrical setup. Tensile result reveals that maximum failure load of 2281.6 N at parameter combination of 900 rpm tool rotational speed, 1.5mm plunge depth, and 3 seconds dwell time, while the minimum failure load of 1060.36N was obtained at tool rotational speed of 1120rpm, plunge depth of 0.5mm, and dwell time of 2s. From post fractured assessment, three modes of fracture occurred at the joints, namely Interfacial - shear fracture mode, interfacial fracture mode (produced the weakest failure load), and complete shear mode (produced the best failure load). This finding has been able to identify the parameters settings required to obtain Al/Cu joints with high electrical conductivity. Dynamic recrystallization of grains (equiaxed grains) is obtained at the stir zone of all joints and grain coarsening ensues in the weld nugget in a progressive manner towards the heat affected zone. The simulated and actual temperature results show similar observation as an increase in rotational speed caused an increase in the peak temperature of the joints. High resistivity value of 0.0440 Ωm (obtained at 900 rpm, 1.0 mm and 2 s) and low value of 0.0233 Ωm (900rpm, 0.5 mm and 1 s) were obtained in the welded Al/Cu joint. Effective parameter combination is a notable approach of improving the mechanical and electrical properties of Al / Cu joint.