Why is alternating current (AC) used for welding aluminum in GTAW?

Using alternating current (AC) for welding aluminum in Gas Tungsten Arc Welding (GTAW) is primarily beneficial because it provides cleaning action and helps prevent oxide formation. Aluminum naturally forms a thin, protective oxide layer when exposed to air, which can hinder the welding process by preventing proper fusion between the aluminum pieces being joined.

The alternating current used in GTAW switches polarity from positive to negative at a specific frequency. During the positive phase, the electrode (often made of tungsten) becomes positively charged, which creates a cleaning action that effectively removes this oxide layer from the surface of the aluminum. This action prepares the metal for more effective welding by ensuring a clean and suitable surface for fusion.

In contrast, direct current would not provide this cleaning action and could lead to improper weld quality due to insufficient penetration and poor bonding of the weld. This is why alternating current is preferred when welding aluminum, allowing for better quality welds and enhanced performance during the GTAW process.