Dissimilar welding of AA5083/AA7039 by self-reacting friction stir welding

To evaluate the potential of similar and dissimilar welding, 3 mm thick plates of 5083 and 7039 aluminum alloys were joined by using the self-reactive friction stir welding technique. The bobbin tool was manufactured from H13 tool steel. The effect of several process parameters such as shoulder pinching gap, transverse speed, and tool rotation speed was investigated in order to design a defect-free joint. Tensile testing indicated that the joint efficiency for connections 5083–5083, 7039–7039, and 7039–5083, respectively, is 94.5, 80.4, and 97.4%. Which are much superior to the joint efficiency of fusion welding procedures and at least as good as, if not slightly better than, conventional friction stir welding. Microscopic investigation of the fracture surface of welded specimens indicated that ductile fracture is the primary failure mechanism for similar joints, whereas minor areas of brittle fracture can be seen for dissimilar joints. The hardness profile of the welded components' cross-sections near the upper and lower shoulders was investigated, and it was revealed that the higher hardness at the lower shoulder is due to the lower temperature of the workpiece in this area.