Enhancing droplet transfer and welding speed in AZ31B magnesium alloy via a novel arc-extinguishing CMT (AE-CMT) welding process

Owing to the importance of weight reduction for improving fuel efficiency, AZ31B magnesium alloy has been increasingly used in automobile bodies. However, conventional Metal Inert Gas (MIG) welding suffers from severe welding spatter, poor arc stability, low efficiency, and a narrow process window, which severely restrict its widespread application. To overcome these problems, a novel Arc-Extinguishing Cold Metal Transfer (AE-CMT) process was developed by introducing an additional arc-extinguishing phase into the conventional CMT process. The droplet transfer behavior and arc characteristics of W33M magnesium alloy filler wire with a diameter of Φ1.2 mm during AE-CMT welding were investigated using a high-speed CCD camera and a waveform recorder. The results indicate that by optimizing the process parameters, a droplet transfer frequency exceeding 120 Hz can be achieved for the Φ1.2 mm diameter W33M magnesium alloy filler wire during the AE-CMT process, within a wire feed speed range of 4.0–14.8 m/min. The maximum droplet size is 1.6 mm, which is much smaller than the critical droplet transfer size of 2.5 mm for magnesium alloys. Additionally, high-quality, continuous 1.5 mm-thick AZ31B butt joints can be obtained at welding speeds of 0.5–3.0 m/min. Therefore, the AE‑CMT process can effectively enhance the droplet transfer frequency and welding speed of magnesium alloys while significantly reducing welding spatter, thereby improving welding efficiency and broadening the welding process parameter window for magnesium alloys. Thus, AE‑CMT is a novel and highly suitable welding method for magnesium alloys.