Step 1: Identify aluminium's stubborn surface problem.
Aluminium naturally carries a thin but tough oxide layer on its surface, and this oxide melts at a temperature far higher than the aluminium metal underneath it, which makes it very difficult to get a clean weld unless that oxide is dealt with first.
Step 2: See how TIG welding is specially set up to handle it.
For aluminium, TIG welding machines are typically run on alternating current rather than straight DC, and this AC waveform alternates between a half cycle that melts the metal deeply and a half cycle where the arc bombards the surface with positive ions, physically knocking the oxide layer off in a self cleaning action.
Step 3: Compare this to welding other metals.
Metals like stainless steel or titanium do not carry this same troublesome refractory oxide, so they are welded with straightforward DC TIG without needing this special cleaning action. Because AC TIG solves aluminium's unique oxide problem so effectively, TIG is especially valued for welding aluminium.
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