Depends ... were they painted or bare metal? I usually don't concern myself blasting stuff that's getting painted but if its bare metal then you want to just clean it. Rust removers work on steel and cast iron. Aluminum cleaners on aluminum.

On aluminum I degrease it, pick away any caked on dirt then I use an acid solution made for aluminum. You cannot let the stuff dry or it will streak, splotch, etc.. Spray it on, scrub it and keep it wet then rinse off. Redo it if necessary. You cold try a flat or satin clearcoat after that.

Available at bodyshop supply places - called Alumiprep. Similar stuff used to be commonly available to clean your wife's steam iron.