Which polarity is preferable when the cleaning action of DCEP is required?

The correct choice emphasizes the use of Alternating Current (AC) as the preferred polarity when the cleaning action provided by Direct Current Electrode Positive (DCEP) is essential. In processes like Gas Tungsten Arc Welding (GTAW), alternating current is particularly advantageous for welding aluminum and magnesium, as it combines both cleaning and penetration effects.

When AC is used, the current periodically switches between positive and negative cycles. The positive half-cycle provides a cleaning action similar to DCEP, effectively removing oxides and contaminants from the surface of the base metal. This cleaning is essential for maintaining a quality weld on materials that typically form an oxide layer, such as aluminum.

While DCEP offers good cleaning action on non-ferrous metals, AC is superior for specific applications and materials as it balances cleaning with effective penetration during the negative half-cycle. Therefore, AC becomes the preferred choice when the specific requirement for cleaning action is needed while also allowing for adequate heat input during welding.