In GTAW of aluminum, why is alternating current (AC) commonly used?

• A. It reduces electrode consumption
• B. It avoids shielding gas usage
• C. It helps break up oxide on aluminum
• D. It increases tungsten life

Answer: (C)

Aluminum oxide forms a stubborn, non-wetting layer on the surface. Using alternating current in GTAW continually reverses polarity, which creates a cleaning action at the arc. This action breaks up and sweeps away the oxide so the molten aluminum can wet and fuse properly to the base metal. The positive half-cycle helps remove the oxide, while the negative half-cycle focuses heat into the metal to melt and fill the joint, giving a stable, clean weld puddle. Shielding gas is still required, and tungsten life isn’t the primary reason AC is used.