I was told a long time ago, regardless or what you are gluing up.... if it's aluminum to aluminum, the paint is in the way. That in actuality would be paint to paint. Painted wood to painted wood..... same thing. If something is coated with layers of paint, the only thing you should be putting on it would be more paint, not glue. If you buy glue that says it's good for this, that or whatever, it doesn't mean paint should be in the middle of the equation. Can ya do it ?? Sure, but it's just not as strong a bond.
Maybe things have changed since I was taught that, but it hasn't failed me yet.