Tensile properties of friction stir welded 7075 aluminum alloy at Room Temperature

Tensile properties of friction stir welded 7075-T6 and 7075-O aluminum alloy joints were investigated at room temperature. After completion of friction stir welding, the joints were subjected to a natural aging treatment and then they were tested by tensile machine. The strength of a T6 joint was less than that of the base material. This result is consistent with a finding that the Vickers hardness of the T6 joint was less than that of the base material. Fracture occurred in the stir zone of the T6 joint, and the fracture morphology of the joint was intergranular. On the other hand, the strength of an O joint was highter than that of the base material. This result is in agreement with a finding that the Vickers hardness of the O joint was higher than that of the base material. Fracture occurred in a thermo-mechanically affected zone of the O joint, and the fracture morphology of the joint was transgranular. The results on tensile elongation showed a tendency that the O joint had lower ductility than the base material. The joint efficiency, which was calculated from the strength, was more than 80% for all joints. In this paper, tensile properties of abovementioned joints at room temperature are discussed from the viewpoint of Vickers hardness and microstructure.