Oxidation? Help needed!

Submitted to General Questions

Late last fall, I attempted to clean my aluminum (at least that's what I think it's made of) storm door. I promised myself that I would attack this problem in the spring, which has arrived!
What is the best solution to clean the door before painting? A neighbor suggested a vinegar solution. Is the door salvageable? How would I proceed with painting? I can afford a new storm door if that's the best option.
Thanks for any help you can offer!