Choosing AC vs. DC for TIG Welding Aluminum

When it comes to TIG welding aluminum, the choice between Alternating Current (AC) and Direct Current (DC) is crucial. The methodology that has emerged as the standard for most aluminum TIG welding applications is the use of Alternating Current (AC). This article will delve into why AC is preferred and the role that DC plays in certain scenarios.

Preferred Method: Alternating Current (AC)

AC is the recommended method for TIG welding aluminum. This is primarily due to the need to clean the aluminum surface by breaking up its oxide layer, which is essential for achieving a high-quality weld. The alternating current between positive and negative charges allows for effective cleaning during the positive cycle and penetration during the negative cycle.

The Challenge of Aluminum Oxide

Aluminum generates an oxide layer almost instantaneously upon exposure to oxygen. This oxide layer has a melting point of 3,762°F, which is over three times higher than that of elemental aluminum at 1,221°F. As a result, the underlying aluminum substrate would have vaporized before the oxide layer could be melted.

TIG Welding With AC

In the AC welding process, the cycle alternates between DC Electrode Negative (DCEN) and DC Electrode Positive (DCEP) current. During the DCEP electrode half of the cycle, the cleaning action blasts away the aluminum oxide layer as electrons flow from the work piece to the tungsten. Conversely, during the DCEN half of the cycle, electrons flow from the tungsten to the work piece, melting the puddle and allowing the bead to fuse and filler to be added, while the shielding gas keeps an oxide layer from forming.

Why DC Welding Fails

Direct Current (DC) welding on aluminum can melt the aluminum, but without the cleaning action, it becomes difficult to form a puddle through the oxide layer. Consequently, the welding process results in less penetration and oxide contamination, potentially leading to gaps and burn-through in the work piece.

Using AC TIG Welding

AC TIG welding, also known as alternating current tungsten inert gas welding, is specifically designed to overcome the challenges posed by aluminum oxide. The electrode positive configuration of AC TIG welding helps remove the oxide layer by "scraping" it off at the arc spot.

Control of AC Balance

For optimal TIG welding on aluminum, a precise balance of the alternating current is required. The AC balance represents the fraction of time the AC remains positive or negative in one cycle and is typically expressed as a percentage. For instance, AC set to 60 electrode negative means the electrode is at a negative value for 60% of the duty cycle, with the remaining time being positive. This balance ensures that the oxide layer is effectively removed while maintaining the integrity of the weld.

To further understand the nuances of TIG welding aluminum, you can watch a detailed video demonstration:

Watch the Video on TIG Welding Aluminum

By harnessing the power of AC in TIG welding, you can achieve the high-quality welds necessary for aluminum applications, ensuring both a clean and strong joint without the issues associated with oxide contamination and overheating common in DC welding.

Conclusion

In summary, ensuring the superiority of aluminum TIG welding, AC is the go-to choice. Understanding the necessary balance and techniques can significantly enhance your welding results and proficiency. By following these guidelines, you'll be able to master the art of TIG welding aluminum with confidence and precision.