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With the rapidly increasing price of copper, electrical equipment manufacturers are going for more and more usage of Aluminium instead of copper (Rohatgi and Weiss, 1977) such as in busbars, heat sinks, panel boards, etc. Various factors influence the choice of conductor material for high current bus system. Generally, copper is selected for one side of the bus system and aluminium for other. Previously, bolted joints were used to make transition joints (William, 1980; and William, 1997). Because of difficulty in making long-term electrically stable bolted joints between aluminium and copper, much investigation has been concentrated on transitions fabricated by bonded Al to Cu materials.
Transition joint made by metallurgical welding of aluminium to copper is widely used to transmit electricity in high current bus systems. From the point of welding technology, aluminium and copper are incompatible metals to welding due to a high affinity to each other at a temperature more than 125 °C and produce intermetallic compounds, which are brittle in nature (Jiahu Ouyang et al., 2006; and Abdollah-Zadeh et al., 2008). These intermetallic components are mechanically and electrically unstable, because they contain a nonmetallic covalence bond. Hence, an attempt was made to weld the Al/Cu, using traditional methods with the application of thermal energy to melt and fuse; the two materials can result an unreliable weld. The general method to obtain this metallic bond is to plate Al with another material that facilitates soldering. This method contains a number of steps, is environmentally unfriendly and is used for only small joints. Solid state joining methods such as friction welding, explosion welding and Friction Stir Welding (FSW) were accepted as the qualified jointing processes (Bekir and Ahmet, 1995; and Behcet, 2008) of Al/Cu materials due to negligible intermetallic formation and relatively good joint interface.
FSW is more flexible, compared to all other solid state welding processes in joining components rather large or complex in shape (Fratini et al., 2007). FSW technology is an emerging thermomechanical solid state welding method, in which melting and recast of joining materials do not take place (Mishra and Ma, 2005). The welding process in this case requires that the parts to be joined are kept in position firmly. A rotating nonconsumable tool with a specially designed shoulder and pin is plunged completely into the overlap surfaces up to the shoulder, touches the joint surface, and traverses along the line of seam, as shown in Figure 1. FSW process offers several advantages such as low manufacturing time, large material saving, joining of similar and dissimilar materials in different thicknesses. The galvanic corrosion of friction stir welded Al/Cu joints is less compared to the mechanical joints. Hence, the FSW process can minimize the thickness of the intermetallic component because it is performed at well below the melting point and using high pressure and low processing time.
The present study focuses on the application of the FSW technology to join aluminium to copper plates in lap joints to be used in electrical and electronics industries. A wide experimental investigation on Al/Cu bimetallic lap joints was carried out by varying the tool geometry and the main process parameters.
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