Why is AC current used for TIG welding aluminum?

Why is AC current used for TIG welding aluminum?

• A. To keep the oxide layer on aluminum constantly removed by alternating polarity and achieve better cleaning and fusion.
• B. Because DC current provides the best penetration for aluminum.
• C. Because AC is cheaper to run.
• D. Because aluminum requires direct current only.

Answer: (A)

Aluminum forms a protective oxide layer that must be removed for a good weld. Using AC for TIG welding provides continuous cleaning action as the arc alternates polarity, breaking up and removing that oxide on each cycle so fresh metal is exposed for fusion. The negative part concentrates heat in the workpiece for penetration, while the positive part helps scrub and clean the surface, preventing oxide from hindering the weld. That’s why AC is used rather than DC for aluminum—the oxide won’t stay out of the way with a steady polarity, so the weld won’t fuse as reliably.

Aluminum forms a protective oxide layer that must be removed for a good weld. Using AC for TIG welding provides continuous cleaning action as the arc alternates polarity, breaking up and removing that oxide on each cycle so fresh metal is exposed for fusion. The negative part concentrates heat in the workpiece for penetration, while the positive part helps scrub and clean the surface, preventing oxide from hindering the weld. That’s why AC is used rather than DC for aluminum—the oxide won’t stay out of the way with a steady polarity, so the weld won’t fuse as reliably.