The best thing to do with aluminum is to anodize it... range of colors clear, champagne, bronzes or hardcoating to get flat black.
The key to painting it, especially powder, is the primer. Even still it wont last forever.
I suspect from what you said they tried to paint over aluminum. If the original aluminum was anodized (most likely, even clear) the paint wont stick well. At my old shop we would strip the aluminum, then process it with alodine, then powder coat. Most places cant alodine, but its the best way to go. Shop is Mathpeth queens.
http://www.henkelna.com/cps/rde/xchg...=8797571448974. Tell s a bit about it more technically.
I can help you out if you want, shoot me a pm
