When welding aluminum with Gas Tungsten Arc Welding (GTAW), what current/polarity is primarily used?

In Gas Tungsten Arc Welding (GTAW), commonly known as TIG welding, aluminum is predominantly welded using alternating current (AC). This is primarily due to the unique properties of aluminum. When aluminum is welded, the AC polarity offers a beneficial cleaning action on the surface of the aluminum. The positive half of the AC cycle cleans the oxide layer that typically forms on aluminum, making it easier to achieve a strong and clean weld.

Additionally, the negative half of the AC cycle allows for effective penetration into the base material, which is crucial for achieving a good fusion and weld strength. This alternating current thus combines both necessary attributes: cleaning and penetration.

While Direct Current Electrode Negative (DCEN) is often used for welding materials that do not have significant oxide layers, and Direct Current Electrode Positive (DCEP) may enhance penetration in other materials, neither is suitable for aluminum welding like AC, which is tailored specifically to address the unique challenges associated with aluminum's properties.