Microstructure and mechanical properties of welds at keyhole closures in variable-polarity plasma arc aluminum welding

The variable-polarity plasma arc (VPPA) keyhole welding technology offers an efficient solution for producing defect-free aluminum alloys, but a keyhole is left at the end of the welding process. Traditional manual TIG welding, which involves filling keyholes, often lacks productivity and can result in inconsistent weld quality, hindering the production of high-strength and high-precision parts. In this study, a keyhole self-closing method was proposed, and the microstructure and mechanical properties of keyholes closed by the proposed method were compared to those closed by manual TIG welding. The results showed that the self-closed keyhole had a smaller fusion line wide, and the weld zone had a uniform distribution of equiaxed crystal, with fewer pore defects. While the manual TIG welding-filled keyhole had a higher density of dislocations, which leads to an increase in the microhardness. The presence of pores in the manual TIG welding-filled keyhole reduces its tensile strength and elongation, which were lower than those of the self-closed keyhole by 61.5 MPa and 5.8 %, respectively. The self-closing method can effectively address the keyhole retention issue in VPPA keyhole welding. By using this method, higher-quality welds with better microstructure and mechanical properties can be produced, which can have important implications for various industrial applications, and in applications where mechanical properties are critical.