Why is thoriated tungsten not preferred for AC welding?

Thoriated tungsten is not preferred for AC welding primarily due to the properties of the tungsten electrode and its performance in alternating current applications. In AC welding, the electrode must effectively clean the surface of materials and maintain a stable arc throughout the welding process.

Thoriated tungsten electrodes are typically favored for DC welding because they have excellent stability and can withstand higher temperatures, which makes them suitable for welding ferrous and non-ferrous metals like stainless steel and titanium. However, in AC applications, particularly when welding aluminum, a different type of tungsten, such as zirconiated or pure tungsten, is often used because these options provide better performance with aluminum's oxide layer that needs to be effectively cleaned.

While the idea that thoriated tungsten performs poorly on thin metal might seem relevant, the main concern in AC applications lies in the stability of the arc rather than the thickness of the metal being worked on. The instability of the arc associated with thoriated tungsten in AC welding leads to difficulties in creating consistent welds, thereby making it less suitable for this type of work. Therefore, the focus should be on the arc stability issues rather than the performance on thin metals.