Is this corrosion?

I just pulled the plastic off after ~2 years and this was underneath:



There was a good bit of residual adhesive over the area that is ?streaked? but that came off with acetone. MEK had no effect either.

I'm guessing it qualifies as very slight surface corrosion. Hit it with a scotchbrite pad (just like you would if it had a mirror like finish) and continue building.

Maybe a slight amount of oxidation, which is technically a type of corrosion but it looks more like residual offgasing from the plastic protective sheet. Take a solvent and see if it wipes off. Otherwise, a light polishing as already suggested will clean it right up.

Or leave it alone. Completely normal for the Alclad to form a light layer of oxide. If you're going to prime, then yeah, I'd hit it with a Scotchbrite.