Friction Stir Lap Welding of Aluminum to Steel Using Refractory Metal Pin Tools

Steel and Al were friction stir lap welded using two different W-25% Re-4% HfC pin tools, having two different pin diameters and pin lengths. The effects of plunge depth, bonding area, and top sheet positions on the microstructure and mechanical properties were investigated. Morphology of the joint interface showed severe steel flash on the retreating side, which controlled the joint strength when the top sheet was placed on the retreating side. A joint efficiency of 58% was achieved when right-handed lap welds were made using the pin tool with longer pin length.