If you want the aluminum to look "new" or "as cast," you'll need to remove the aluminum oxide from the part(s). That requires an etching acid. Consumer grade wheel cleaners work fine. I use Meguire's Chrome Wheel Cleaner with a stiff brush, then rinse with water. Add baking soda to the water to neutralize the acid if you're worried about it, but in my 40+ years of cleaning, I never have.
