Which polarity is used for welding magnesium in GTAW?

When welding magnesium using Gas Tungsten Arc Welding (GTAW), alternating current (AC) polarity is preferred. This is because AC allows for more efficient cleaning action on the oxide layer that forms on the surface of magnesium. The alternating current switches between positive and negative polarity, which helps in removing the oxide film during the positive phase while enabling better arc stability during the negative phase.

The unique characteristics of magnesium require this dual action provided by AC, making it effective in achieving good weld quality and penetration. The benefits of using AC can be critical for magnesium since its oxide layer can be quite tenacious, and it must be cleaned to ensure a strong bond.

In contrast, DC electrode positive (DCEP) and DC electrode negative (DCEN) do not provide the same cleaning action that AC does, limiting their effectiveness for magnesium welding. While DC can be useful for welding other materials, for magnesium specifically, AC is the optimal choice.