Spray Finishing Aluminum
From contributor S:
Tough situation - aluminum is a different critter. As with any paint job, the initial surface must be absolutely clean and free of any oils.
When extruded aluminum is "raw", it is very porous. I suspect there are many treatments designed to fill the pores, all of which have the potential to affect your paint job. At the very least, the aluminum will have oils and milling fluids imbedded in the pores. I suspect most milling/cooling oils used are water soluble - soap and water should break it down.
If the extruded aluminum was anodized (a process where pores are filled), then you have a situation where your new finish may not be compatible with the anodize finish. I do not know about cast aluminum (picture a motorcycle engine), but I suspect cast would be much less porous than extruded. They electrostatically apply and bake paint onto cast aluminum all the time. You need to know more about the aluminum itself and how it may have been treated before you got it. Many automobiles over the years have had aluminum sheet metal body parts - sheet aluminum is an extruded product. A visit to your favorite body shop might be worth your time.
Brake cleaner - available at AutoZone - is a very effective remover of oils from metals. It seems to cut everything and evaporates very quickly. Also, some good old lacquer thinner would likely work as well. All this to say "clean it, clean it, clean it, clean it some more, and then experiment".
From contributor R:
Aircraft guys do this all the time. I worked at Stits Polyfiber coatings for a while in my youth and they use Aluma-Dyne E-2300 conversion coating which is a chromic acid solution for clear coating aluminum and Aluma-Dyne E-2310 phosphoric acid etch/brightener which is an etch for painting.
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