What is the reason for using AC when TIG welding aluminum?

• A. It alternates cleaning action and penetration
• B. It increases travel speed
• C. It reduces shielding gas consumption
• D. It improves weld appearance

Answer: (A)

Aluminum forms a tough oxide layer that prevents fusion if not removed during welding. Using alternating current in TIG welding switches the arc polarity between electrode positive and electrode negative. In the positive half-cycle, the arc cleans the oxide surface by removing or breaking up the oxide, exposing fresh metal. In the negative half-cycle, the arc concentrates heat into the base metal, giving good penetration and fusion. The combination of cleaning action and penetration is what makes AC TIG welding of aluminum effective and yields sound welds.

Other options don’t hit the main reason: travel speed, gas usage, and appearance may be affected by welding setup, but they aren’t what AC specifically provides for aluminum—its essential benefit is the alternating cleaning action plus penetration.