Making the paint stick and stay put on aluminum is the tricky part. Back before the tree huggers got their manties in a wad about the chemistry, zinc chromate primer was the "go to" method for preparing aluminum for paint. Airplanes all over the world, including virtually everything the US Air Force flew, got coated in zinc chromate before the color coat got applied. I'm pretty sure there's some sort of acceptable substitute nowadays, but it's probably not as effective.
Jerry
