Effect of gas pulse parameters on the arc characteristics and weld quality of pulsed plasma gas variable polarity plasma arc welding

To enhance the reliability of aluminum alloy welding quality, this study investigates the effects of gas pulse parameters on the arc characteristics and weld quality in pulsed plasma gas variable polarity plasma arc welding(PPG-VPPAW) of 5051 aluminum alloy. Results showed that increasing the gas duty cycle enhanced arc pressure fluctuation but reduced average arc pressure. When the duty cycle exceeded 1/2, excessive pressure fluctuations destabilized the weld pool. Arc voltage fluctuations also intensified with larger duty cycles, reducing arc heat input and stability. Severe variations in arc divergence and high-temperature area were observed at duty cycles above 1/2, leading to poor heat transfer. Weld morphology confirmed these findings: duty cycles of 1/5 and 2/5 produced uniform surfaces with dense fish-scale ripples, while 3/5 and 4/5 introduced defects such as humping and undercut. Mechanical testing showed that conventional variable polarity plasma arc welding(VPPAW) joints reached 262 MPa tensile strength and 18.3 % elongation, corresponding to 79.8 % and 85.1 % of base metal values. At a duty cycle of 2/5, the tensile strength increased to 297 MPa and the elongation to 21.5 %, representing the best overall performance. Variations in the gas pulse frequency did not significantly affect the average arc pressure or arc voltage. However, as the gas pulse frequency decreased, the fluctuation frequency of the arc pressure and arc voltage also decreased, while the fluctuation amplitude of the arc voltage increased. At 8 Hz, the tensile strength and elongation increased by 13.4 % and 17.5 %, respectively, compared with lower frequencies(4 and 2.6 Hz).