What is the significance of AC in GTAW when welding aluminum?

In Gas Tungsten Arc Welding (GTAW), particularly when welding aluminum, alternating current (AC) holds significant importance due to its ability to effectively break up the oxide layer that naturally forms on the surface of aluminum. This oxide layer is a key challenge in aluminum welding because it has a higher melting point than aluminum itself. When using AC, the current alternates between positive and negative polarities, which plays a crucial role in the welding process.

During the positive phase of the AC cycle, the electrode becomes positive, allowing it to effectively clean the surface by oxidizing the aluminum oxide layer. This cleaning action is essential for achieving a strong and clean weld. Conversely, during the negative phase, the electrode produces a more focused heat, which helps in properly melting and fusing the aluminum base metal. The ability of AC to alternate between these two phases makes it ideal for welding aluminum, resulting in better overall weld quality and integrity.

The other choices, while they present various aspects of welding dynamics, do not capture the critical role of AC in overcoming the specific challenge posed by the aluminum oxide layer, making the second option the most accurate and complete understanding of AC's significance in GTAW for aluminum.