What specific current type and polarity would an expert select for Gas Tungsten Arc Welding of aluminum, and precisely why does this choice minimize oxide contamination?

For Gas Tungsten Arc Welding (GTAW) of aluminum, an expert would specifically select Alternating Current (AC). Within this AC waveform, the polarity continuously switches between Electrode Negative (EN) and Electrode Positive (EP). This choice minimizes oxide contamination primarily due to the Electrode Positive (EP) half-cycle, which provides a critical "cleaning action." During the EP phase, the tungsten electrode becomes positively charged, and the workpiece becomes negatively charged. Electrons flow from the workpiece to the electrode. Simultaneously, positively charged gas ions from the inert shielding gas, such as argon, are accelerated from the positively charged electrode towards the negatively ....