Effects of Forces on the Welding Tool during the Dissimilar Joining of Aluminium and Copper

In 1991, a game changing technique was introduced into the metal joining community. Patented in 1991 by The Welding Institute, the Friction Stir Welding (FSW) process has since transformed the way metal joining is being done. Since then, many industries have come to embrace the new joining technology due to its ease of operation and other numerous advantages it offers. Aside from the ease with which it is employed to join similar metals, FSW provides a way of joining dissimilar metals at the microstructural level without some of the problems that traditional metal joining technologies (especially fusion welding) encounter. As metals of choice in the engineering community due to their numerous advantages, a lot of attention have been given to both aluminium and copper by the research community. FSW has been used extensively to join both metals individually without much difficulties. Both metals have also been successfully joined together using the butt welding configuration. However, little successes have been recorded for the lap welding of both metals using the FSW technology. Research has shown that the relationship between the input and output processing parameters influence the quality of the produced welds. The choice of tool geometry, tool design, tool pin as well as the tool shoulder profile have been shown to be important in determining the weld quality. However, the effects of the forces of the welding tool on the quality of Friction Stir Welds have not been fully understood. This present work reports the relationship between the forces of the tool during welding on the quality of the produced welds during the Friction Stir Lap Welding of 3 mm plates of aluminium and copper. While the welds produced were fraught with defects, it is observed that the force of the tool was proportional to the size of the defect produced in the welds. The weld data from the FSW machine was used in determining this relationship while the produced weld integrities were tested for microstructure and the results are reported and discussed.