Study of keyhole closure and analysis of microstructure and mechanical performance of weld joints for variable polarity vertical up plasma arc welding process

Two technical approaches for keyhole closure were conducted. Workpieces of aluminium alloy 2219 were welded using variable polarity vertical up plasma arc welding technology. Effects of welding process parameters on keyhole closure were analysed. Appropriate technical criteria for keyhole closure in the welding of aluminium alloys (3 or 6 mm in thickness) via the variable polarity vertical up plasma arc welding technique were obtained. Experimental simulation of girth welding (overlap welding) was conducted using the appropriate process parameters for the keyhole closure stage of plate butt welding, and the feasibility of circumferential welding was verified. Accordingly, girth welding of the external tank of a carrier rocket was achieved using the appropriate parameters for the keyhole closure technique. In addition, the metallurgical process and mechanical performance for the single pass and overlap welds were analysed and compared.