Al-to-Cu Friction Stir Lap Welding

Abstract

Recently, friction stir welding (FSW) has been used frequently to join dissimilar metals, for instance, Al to Mg, Cu, and steel. The formation of brittle intermetallic compounds often severely limits the strength and ductility of the resultant welds. In the present study, Al-to-Cu lap FSW was studied by welding 6061 Al to commercially pure Cu. Conventional lap FSW was modified by butt welding a small piece of Al to the top of Cu, with a slight pin penetration into the bottom of Al. At travel speeds up to 127 mm/min (5 ipm), the modified welds were about twice the joint strength and five to nine times the ductility of the conventional lap welds. In the conventional lap welds, voids were present along the Al–Cu interface, and fracture occurred along the interface in tensile testing. No such voids were observed in the modified lap welds, and fracture occurred through Cu. Thus, as in the case of Al-to-Mg lap FSW recently studied by the authors, modified lap FSW significantly improved the weld quality in Al-to-Cu lap FSW. At the relatively high travel speed of 203 mm/min (8 ipm), however, modified lap FSW was no longer superior because of channel formation.