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.

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It is known that it is difficult to bond dissmilar metals such as the aluminum and copper using diffusion bonding, because an intermetallic compound is easily produced in the bond interface. CD stud welding is suitable for welding of the bolt to the sheet without weld-marks on the back side of the weld. In this study, we performed stud-welding of bolts made of copper to an aluminum plate and investigated its weldability. The mixed layers were formed by melting of aluminum and copper at welded zone between the aluminum plate and the copper stud bolt. Tensile fractures of the stud welds were occurred in the intermetallic compound and/or the interface between the intermetallic compound and the mixed layer. High weld strength of 2.51 kN was obtained in case of capacitor capacity of 18.8 mF and charging voltage of 140 V.

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An unified numerical simulation model of AC TIG welding of the aluminum plate considering energy balance among the electrode, the arc and the base metal and employing an analytical model for calculating cleaning rate of the oxide layer has been developed for investigating heat transport properties and weld pool formation process in AC TIG welding of aluminum plate. As a resullt of this simulation, it was shown that although the heat flux from the arc onto the base metal increases in EN (Electrode Negative) phase due to the electron condensation, that in EP (Electrode Positive) phase conversely decreases because mainly of cooling caused by the electron emission. Furthermore, the validity of the simulation model was confirmed by comparing to experimental results such as the arc voltage, the area of cleaning zone and the shape of weld pool.

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