Which statement best describes the effect of an oxide layer on aluminum weld quality?

• A. It can contribute to porosity and hinder fusion.
• B. It strengthens the weld.
• C. It has no effect.
• D. It prevents cracking.

Answer: (A)

Aluminum’s oxide film is a surface barrier that interferes with welding. This oxide has a much higher melting point than aluminum, so it doesn’t melt and fuse with the base metal. When the weld pool forms, the oxide can prevent clean metal-to-metal contact and proper wetting, leading to incomplete fusion. Fragments of oxide can also become trapped in the molten metal and later solidify as porosity. So the oxide layer can both hinder fusion and contribute to porosity, which is why surface cleaning and good shielding are essential for aluminum welding.