Effect of Heat Input on the Electrical Resistivity of Dissimilar Friction Stir Welded Joints of Aluminium and Copper Akinlabi E.T, Madyira, D. M., Akinlabi, S.A Dept. of Mechanical Engineering Science, University of Johannesburg, P.O. Box 524, Auckland Park, 2006, South Africa, Email: etakinlabi@uj.ac.za Abstract—This paper reports the effect of heat input on the resulting electrical resistivities of joints between aluminium and copper produced with the friction stir welding process. Welds were produced using three different shoulder diameter tools, viz: 15, 18 and 25 mm by varying the rotational speed between 600 and 1200 rpm and the traverse speed between 50 and 300 mm/min in order to vary the heat input to the welds. The microstructures of the joint interfaces were characterized, and the electrical resis- tivities measured. The resulting microstructural characterization revealed that metallurgical bonding was achieved at the joint interfaces of the welds produced. It was also observed that the electrical resistivity of the joint increased as the heat input to the welds increases. Index Terms—Friction Stir welding, Microstructure, Electrical resistivity I. I NTRODUCTION Friction Stir Welding (FSW) is a solid-state joining tech- nique invented and patented by The Welding Institute (TWI) in 1991 for butt and lap welding of ferrous and non-ferrous metals and plastics [1]. Since its invention, the process has been continually improved upon as its scope of application becomes expanded. FSW is a continuous process that involves plunging a portion of a specially shaped rotating tool between the butting faces of a joint. The relative motion between the tool and the substrate generates frictional heat that creates a plasticized region around the immersed portion of the tool. In addition, the shoulder prevents the plasticized material from being expelled from the weld. Therefore, the tool is moved relatively along the joint line, forcing the plasticized material to coalesce behind the tool to form a solid-phase joint [1]. Figure 1 illustrates the process definitions for the tool and work piece. The advancing side is on the right, where the tool rotation direction is the same as the tool travel direction (opposite the direction of metal flow), while the retreating side is on the left, where the tool rotation is opposite the tool travel direction (parallel to the direction of the metal flow). The tool serves three primary functions; the heating of the workpiece, the movement of material to produce the joint, and the containment of the hot metal beneath the tool shoulder[1]. The heat generated during the FSW process is often as- sumed to occur predominantly under the shoulder; due to Fig. 1. Schematic diagram of the Friction Stir Welding process [2] its greater surface, and to be equal to the power required to overcome the contact forces between the tool and the workpiece [3]. To an extent, the heat input into the welds increases as the shoulder diameter increases [4]. The three different shoulder diameters used in this research study were chosen to vary the heat input into the welds while varying the process parameter settings. The benefits of this technology include: low distortion, greater weld strength compared to the fusion welding process, little or no porosity, no filler metals, no solidification cracking, no welding fumes or gases, improved corrosion resistance, and lower cost in production applications. Because of the many demonstrated advantages of FSW over fusion welding techniques, the commercialization of FSW is progressing at a rapid pace [5]. FSW is considered to be the most significant development in metal joining techniques in decades; and it is, in addition, a “green technology” due to its energy efficiency, environmental friendliness and versatility. When compared with the conventional welding methods, FSW consumes considerably less energy and no harmful emissions are created during the welding process [6]. High quality joints between Aluminium (Al) and Copper (Cu) will promote the use of such joints in industrial applications, especially in the field of electrical components. Aluminium (Al) and Copper (Cu) are widely applied in engineering structures due to their IEEE Africon 2011 - The Falls Resort and Conference Centre, Livingstone, Zambia, 13 - 15 September 2011 978-1-61284-993-5/11/$26.00 ©2011 IEEE