Direct current (DC)
Direct current (DC) flows in the same direction during welding. For TIG welding copper and steel, the electrode is connected to negative so that heat goes into the workpiece. For overlay welding with aluminum bronze, DC is possible but gives more dilution than AC.
What Direct Current Is
With direct current (DC), the current flows steadily in one direction. In TIG welding, you connect the electrode to positive or negative depending on the material.
DC for Copper and Steel
Copper and steel are welded with DC, electrode negative – the arc puts the heat into the workpiece, keeping the electrode cool. That's standard for most TIG work.
DC for Overlay Welding Aluminum Bronze
Aluminum bronze can also be applied to steel with DC. However, DC gives more dilution: more base metal gets into the weld, the color becomes duller, and the self-lubricating property gets somewhat watered down. If you want the full property and the shiny gold weld, use AC.