| Plasma-MIG welding process, which is superior over regular metal-inter- gas arc welding (MIG) process on the aspects of reducing porosity and achieving finer grains in welding aluminum alloys, can be regarded as a synthesis of plasma welding and gas-metal-arc welding (MIG).In this study, a nozzle-plasma-MIG welding torch, in which the nozzle acted as the plasma anode and the vital parts were directly cooled with water, was designed and had the improvements on the current capacity and life of the quick wearing parts. Moreover, an experimental system of plasma-MIG welding process was set up on the ground of the torch.The mechanism of porosity formation in welding Al-alloy was analyzed and the influences of welding process parameters consisting of wire speed,wire potential,plasma current,welding speed,plasma gas flow rate and shielding gas flow rate on the porosity were studied through an orthogonal experimental scheme taking into account experimental error at the same time. The experimental results demonstrate that the influences of plasma gas flow is remarkable, the weld speed and wire potential take the second place. According to the synthetical analysis, the optimum plasma-MIG process specification of little porosity welding was obtained.In this paper, 10 mm thick 5A06 aluminum alloy was butt welded with the above plasma-MIG welding process parameters, X-ray was adopted to nondestructively test the welding seams and very little porosity was inspected; the tensile strength and toughness of the Plasma-MIG welding were both higher than that of the two-pass MIG welding by comparing the mechanical properties of welded joints, and the fracture and the microstructure were also analyzed. In addition, the high melting rate welding of 10 mm thick 5A06 aluminum alloy was also studied, the wire feed rate and the melting rate come to 14.5m/min and 80g/min respectively on the premise that the tensile strength and the toughness of the weld meeted the requirements.
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