What polarity is used when welding aluminum with GTAW?

When welding aluminum with GTAW, alternating current (AC) is the preferred polarity. This is primarily because aluminum, as a material, presents unique challenges due to its tendency to form an insulating oxide layer on its surface. The use of AC allows for effective cleaning of this oxide layer, as the alternating current switches between the positive and negative phases.

During the positive half-cycle of AC, the electrode acts as the anode, which helps to effectively remove the oxide layer by producing a cleaning action on the surface of the aluminum. During the negative half-cycle, the electrode is the cathode, which provides the heat necessary for melting the base material and the filler rod. This combination ensures a stable arc and good fusion between the aluminum pieces being welded.

In contrast, utilizing direct current, whether in the electrode negative (DCEN) or electrode positive (DCEP) configuration, would not adequately address the oxide layer on aluminum, leading to poor weld quality and inadequate penetration. Therefore, AC is essential for achieving successful and high-quality welds on aluminum using GTAW.