Which of the following metals is not typically welded using DCEN polarity?

Using DCEN (Direct Current Electrode Negative) polarity in welding allows for greater penetration and a concentrated heat zone, which is beneficial for certain metals. Mild steel and stainless steel are commonly welded with DCEN because this polarity provides the appropriate heat for effective fusion and penetration. Titanium, while more complex, can also be welded with DCEN due to its requirements for penetration and heat control.

Aluminum, on the other hand, is typically welded using AC (Alternating Current) polarity or DCEN with additional considerations. AC welding is preferred for aluminum because it allows for the cleaning action generated by the positive electrode, which helps to remove the oxide layer that forms on aluminum. If only DCEN is used with aluminum, there is a risk of inadequate cleaning and poor weld quality because the oxide layer hinders proper fusion between the weld and base metal. Therefore, aluminum is not typically welded using DCEN polarity, making it the correct answer in this context.