I bought some etching paint for an aluminum rack for my ATV but is still didn't stick as it should have. I bought it from an auto paint store and paid a pretty penny for the aresol can of the stuff. Don't have an answer for ya, as mine only looks fair.
I used to work on Aluminum boats and there is only one true way. You will need to scuff up the old paint, Zinc Chromate, and Paint. The Zinc Chromate was pulled off the market in quanity a while back but you can find some places that sell a less harmful Zinc Chromate in the area. Make sure to scuff up the old paint before applying. If the aluminum is bear you can use an acis etching instead of sanding.
in 1983 i painted my jon boat its still holding ! sand it , wipe it down with vinegar let it dry for a day shoot it with zinc c primer and the paint is enamel from the parts house our can get flattener for it . the vinegar acid etches the boat and makes the ZC primer grab good (one of those wise old men tricks works great on rusty hand tools too just soak em for a few days )