Products like this acid-etch aluminum-oxide from the surface of aluminum. It forms much like rust (iron oxide) on steel, but it is non-porous so once there it protects against further oxidation forming. It’s the stuff that rubs off gray colored on your skin on old aluminum. When you are done etching and polishing, follow up with a protective coating to keep aluminum oxide from forming again. A good waterproof automotive wax applied occasionally will do. I’ve heard of clearcoat paint being sprayed on, but do your homework to be sure it’s compatible with aluminum.
Here is one product: https://www.wholesalemarine.com/toon-brite-protective-clear-coat-for-boats-35339.html
Dave
