[_paralyzed_]

you gotta sand and sand and sand. (that was really fun to type) First with the coarsest grit necessary to remove the deepest scratches, but not too coarse so as to cause any even deeper scratches. Then switch to finer and finer grades of sandpaper until you're glass smooth. Wet sanding helps as aluminum loads up easily on sandpaper.

Then start polishing. Find a polishing compound and use a dremel with a buffing wheel and polish the crap out of it.

If you want it to stay shiny clearcoat it, otherwise it will oxidize.