Final answer:
The most common welding current for welding aluminum with the GTAW process is Alternating Current (AC) because it provides a cleaning action essential for breaking up the aluminum oxide layer. Option A is correct.
Step-by-step explanation:
When welding aluminum with the Gas Tungsten Arc Welding (GTAW), also known as Tungsten Inert Gas (TIG) welding process, the most commonly used type of welding current is Alternating Current (AC).
Alternating current is preferred for welding aluminum because it allows the cleaning action to occur on the surface of the aluminum, breaking up the oxide layer that can otherwise inhibit the welding process. This process is distinct in comparison to Direct Current (DC), which flows in only one direction and is constant.
The DC options, Direct Current Electrode Negative (DCEN) and Direct Current Electrode Positive (DCEP), do not provide this essential cleaning action for aluminum welding. In addition, Pulsed Current (PC) can be used for certain applications to help control heat input, but it is not the most common for aluminum.