Cathodic Cleaning
The effect in AC TIG welding where positive ions break up and remove the oxide layer on aluminum materials. This enables clean wetting of the weld joint without chemical fluxes.
When TIG welding aluminum, the AC phase does the cleaning. In the half-cycle where the workpiece is the anode, stubborn oxide layers are removed from the surface. This is important because aluminum oxide has a much higher melting point than the base material and would otherwise contaminate the weld. You can recognize the cleaning action by the dull, silvery appearance and the typical hissing of the arc. If the setting is not clean, you won't get proper wetting and the bead won't 'ball up' correctly. Adjust the balance to get enough cleaning without overloading the tungsten.