Research on arc oscillation promoting mass transfer and metal deposition forming in underwater wet welding processes

Currently, research on arc oscillation technology in underwater wet welding remains limited. To improve welding quality, this study employs high-speed imaging to compare the droplet transfer characteristics and arc-bubble dynamics before and after arc oscillation in both underwater and onshore environments. Using welding environment and arc oscillation parameters as variables, the effects and underlying mechanisms of arc oscillation on weld formation quality, microstructural evolution, and joint performance were systematically analyzed. The results show that in underwater wet welding, the molten pool is constrained by the cooling and disturbance effects of the water environment, leading to poor weld formation and limited metal spreading. After applying arc oscillation, the droplet transfer frequency increased, particularly showing a 12.5 % improvement under underwater conditions. The weld formation quality was significantly improved, especially in underwater wet welding, with the coefficient of variation of weld width and reinforcement height decreasing by 59.1 % and 24.4 %, respectively. In underwater wet welding, arc oscillation effectively enhanced the flowability of the molten metal and improved the spreading behavior, reducing the spreading angle from 56° to 49°. A smaller spreading angle facilitates subsequent multi-pass metal deposition. Additionally, arc oscillation significantly altered the penetration profile and promoted more uniform mixing of alloying elements. The coefficient of variation for the distribution of each alloying element in underwater arc oscillated welds was decreased by nearly 50 %.