Abstract: Friction-stir welds(FSW) of spray formed 7475 aluminum alloy plate with 4 mm thickness were studied. The shapes and dimensions of FSW tools as well as welding parameters were optimized based on mechanical tests and micro-analysis. Experimental results show that good-appearance welds can be achieved by optimal welding parameters. However,fin and groove defects appear if the welding parameters are not appropriate. It also shows that the mechanical properties of the joints are affected by the welding parameters. Some relations between the mechanical properties and the welding parameters were established. As the rotating speed is 1200 r/min and the welding speed is 80 mm/min,the good weld is achieved and the tensile strength of the weld reaches 442 MPa.