Aluminum needs to be primed with self etching primer (Wallmart auto) then once you apply paint set the can in hot water for 20 seconds, much better spray, sand lightly 800 or 1000 grit between, , finally after last coat of paint ( 3 or 4 layers extremely thin) sand very very light then apply a automotive clear coat. That process will work, stick with Krylon paints or go with more expensive auto spary paints.