You won’t get paint to stick to the aluminum unless you do some specific prep work. All aluminum oxidizes almost immediately, so even if you sand it prior to laying down a coat of primer it oxidizes before you have time to pick up the rattle can. The oxidized layer is what keeps the paint from adhering long term. To do it correctly, and have a chance of a lasting finish, there are aluminum chemical cleaning and prep products on the market which convert the surface to something that paint will adhere to. I’ve done it before, and here is the stuff I used if you are interested.
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