BLACK STAIN (HYDRATED ALUMINUM OXIDE) REMOVAL

I buy and sell secondary coated steels (galvanized, aluminized, etc). I bought about 30 tons of steel coils that exhibit a black, pronounced stain that I need to remove.
The black stain appears along most of the surface of the steel. The steel is commercially called Galvalume (an Aluminum/Zinc coating is applied continuously to the steel. The black stain is likely the result of long term oxidation (steel got wet).
Are there products commercially available that may remove the stain?
Is mechanical removal of the stain possible?
Are there proven methods to remove such a "hard" dark stain?- even if removal is only partial.
Are there companies that provide such stain removal service?
Regards,

If the stain is aluminum oxide, sodium hydroxide should be able to remove it easily without (I believe - test it yourself first) hurting the steel to any significant degree.

If you don't have NaOH handy, but you want to test the idea before sending it to someone who does, try some oven cleaner ⇦ on eBay or Amazon [affil link] .

adv.
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