Effect of Heat Input on the Properties of Dissimilar Friction Stir Welds of Aluminium and Copper

Th is paper reports the effect of heat input on the resulting properties of joints between aluminiu m and copper produced with the friction stir weld ing process. The welds were produced using three different shoulder diameter tools, viz: 15, 18 and 25 mm by varying the rotational speed between 600 and 1200 rp m and the traverse speed between 50 and 300 mm/ min in order to vary the heat input to the welds. The microstructures, the grain sizes and the microhardness of the joint interfaces were characterised, and the electrical resistivities o f the jo ints were also measured. The resulting microstructural characterizat ion revealed that good metallurgical bonding was achieved at the jo int interfaces of the welds produced; this is evident with the presence of interlayers of aluminiu m and copper observed in the stir zones of the welds. The grains at the interfacial regions were recrystallized leading to a sharp decrease in the grain sizes compared to the parent materials. Higher Vickers microhardness values were measured at the joint interfaces resulting fro m strain hardening and the presence of intermetallics. It was also observed that the electrical resistivities of the jo ints increased as the heat input to the welds increases.