What polarity is used when welding Aluminum?

• A. DCEN
• B. DCEP
• C. AC
• D. Pulse

Answer: (C)

Using alternating current is essential for aluminum welding because aluminum quickly forms a stubborn oxide layer that blocks proper fusion. The TIG arc with AC reverses polarity, providing a cleaning action during one half-cycle and concentrated heating during the other. This continual cleaning of the oxide and stable heating allow the weld to fuse correctly and avoid porosity or lack of fusion. DC polarities would not deliver that oxide-reducing action, making it harder to achieve a sound weld on aluminum. The term “pulse” describes a current waveform rather than polarity, so it doesn’t specify the necessary polarity for aluminum welding.