Experimental and numerical investigations of friction stir welding of aluminum to copper

In this paper, results of performing successful butt-welding of aluminum grade Al6061-T6 to commercial pure copper using the relatively new friction stir welding (FSW) process are presented and discussed in conjunction with finite element results. A sound weld joint between these dissimilar materials has been achieved only when the pin tool was offset a certain distance from the center of the weld line and the harder material (copper) was placed at the advancing side of the FSW tool. On the other hand, the tool offset was not required when joining the similar materials of aluminum to aluminum and of copper to copper. A combined use of temperature distribution of the aluminum to copper weld nugget determined by a finite element model, the elemental concentration of copper and aluminum in the weld nugget from EDS analysis, and aluminum-copper phase diagram have been used to identify the phases present in the different weldment zones. The aluminum-copper joint was found to consist of several single and two phase intermetallic compounds such as Al₂ Cu, Al₄ Cu_9, and (Al + Al₂Cu). The results revealed higher hardness values for the weld nugget compared with the two base metals.