A welder is performing GTAW on 6 mm thick aluminum plate using an inverter power source in AC mode. They notice that the molten weld pool appears dull, heavily oxidized, and resists forming a smooth bead, despite attempts to increase cleaning action with AC balance. What could be the underlying issue, even with proper AC balance settings?

Question: A welder is performing GTAW on 6 mm thick aluminum plate using an inverter power source in AC mode. They notice that the molten weld pool appears dull, heavily oxidized, and resists forming a smooth bead, despite attempts to increase cleaning action with AC balance. What could be the underlying issue, even with proper AC balance settings?

Answer options:

• The welding current is too low for the material thickness. ✅ The shielding gas contains impurities or is the wrong type for aluminum.
• The base metal has a high concentration of magnesium.
• The tungsten electrode is too large in diameter.

Correct answer: The shielding gas contains impurities or is the wrong type for aluminum.

Explanation: Even with optimal AC balance, an oxidized weld pool in aluminum GTAW strongly suggests contamination from the shielding gas itself. Impurities in the argon or using an incorrect gas can lead to poor puddle control, oxidation, and a dull appearance, as the gas fails to adequately protect the molten metal.