Study of friction stir welding of aluminum

A half-cold hardening aluminum plate were friction-stir welded at various rotation speeds (850–1860 rpm) and travel rates of 30 to 160 mm/min with welding forces ranging between 2.5 and 10 MPa using different dimension welding heads. Experimental results show that the dimensions of the welding head are critical to produce sound welds. The microstructure of the weld is characterized by its much finer and equiaxed grains as contrasted with the coarse and band-like structure of the parent aluminum plate. Tensile strength of the welds is about 20% lower than that of the hardening aluminum plate, but about 10% higher microhardness is demonstrated by the welds in comparison with that of the aluminum plate in annealing condition. Moreover, travel rate of the welding head pin has a strong effect on microhardness and tensile strength of the FSW welds, and the ratio of rotation speed and travel rate of the head should be in a reasonable range to obtain high performance welds. The variables of the welding process are also discussed in terms of heat balance and energy input of the welds.