This is just my 2 cents worth, based on a lot of years metal finishing,
treating, polishing
mild steel shouldn't be treated with anything other than phosphoric acid .
The other acids are too agressive and leave the surface "active" which promotes
VERY RAPID oxidation even after being neutralized.
Aluminum should be treated with mild phosphoric acid or a very mild alkaline
solution and neutralized immediately after removal from the strip tank.
Aluminum DISAPPEARS quickly in strong alkaline solutions.
Stainless steel cane be cleaned in either an acid or alkaline solution
effectively. phosphoric acid at 140d egrees F and a mild electric current does
an excellent job of electropolishing stainless. The parts need to be
neutralized and rinsed.
Stainless steel can also be passivated in a strong nitric acid solution to help
prevent rusting when in contact w/ mild steel.
Tommy
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