What power type should be used with aluminum and magnesium?

• A. DC
• B. DCEP
• C. AC
• D. DCEN

Answer: (C)

Using alternating current is preferred for welding aluminum and magnesium because their oxide layers form quickly and can prevent proper fusion. The AC cycle continuously reverses polarity, which provides a cleaning action at the surface during the weld. This helps break up and blow away the fragile oxide layer as the arc starts, allowing the molten metal to fuse smoothly with the base metal. The heat distribution also alternates with the polarity, giving stability to the arc and better control over penetration, which is especially important for these reactive metals.

Direct current methods don’t offer that built-in surface cleaning action, so oxide can remain at the arc zone, leading to porosity or poor fusion. For that reason, AC is the best choice for aluminum and magnesium, while DC variants are more common when welding other metals.