What polarity is used for GTAW of magnesium?

For the Gas Tungsten Arc Welding (GTAW) of magnesium, alternating current (AC) is the preferred polarity. This is due to several factors related to the properties of magnesium and the welding process.

Magnesium is a reactive metal that can be challenging to weld. AC polarity allows for the benefits of both positive and negative phases during the welding process. The positive phase helps to clean the oxide layer that forms on the surface of magnesium, effectively removing impurities that could lead to poor weld quality. Meanwhile, the negative phase contributes to better penetration and heat input into the base metal. This combination of effects is crucial to achieving strong and clean welds in magnesium.

Using DC+ or DC- is less appropriate for welding magnesium because while DC+ can be useful for some metals, it does not provide the cleaning action necessary for magnesium, and DC- may result in excessive heat input, leading to distortion or burn-through. Pulsed DC, while it can be beneficial in some applications, does not replace the efficiency and effectiveness of AC for magnesium specifically. Thus, AC is the most effective and widely accepted method for welding magnesium in GTAW processes.