Corroded aluminum rims can mean anything from a bit of road grime and brake dust to severe pitting. How much time and effort it will take to clean your corroded rims depends totally on how badly corroded they are and what type of corrosion is present. Oxygen is one of the enemies of aluminum. Simply leaving your rims exposed to the air will cause them to turn dull and look shabby. Add in road salts and grime, brake dust and other contaminants and your bright, shinny aluminum rims can start looking really nasty. Once your rims are looking good, they need to be protected from the air.
Hose off your rims with a hard stream of water and apply a liberal amount of liquid dish soap. Allow the soap to soak in for no more than 5 minutes and then hose it off with a strong stream of water. Wipe your rims dry with a good terry cloth. Don't be afraid to use a little elbow grease. This should remove most of the surface grime and allow you to get closer to the real corrosion.
Mask off painted areas of your vehicle using painter's masking tape and sheets of plastic. Then spray Easy-Off oven cleaner on your rims and allow it to soak in for 20 to 30 minutes. Scrub with a Teflon-safe dish-washing scrubber. Hose off with a strong stream of water and immediately buff with a clean terry cloth rag. Again, don't be afraid to use a little elbow grease. Repeat this step if necessary. For many types of corrosion this is all that is necessary. Polish your rims with a commercial aluminum brightener available at your auto supply store and then polish with a clear car wax. If your rims are still corroded, go to the next step.
Sand any pitted areas with 400-grit sandpaper. For many types of pitting this is, unfortunately, the only solution. Sanding can be done by hand or, for large areas, a small sanding wheel on a drill can be used, but be certain not to apply too much pressure and to keep the wheel moving so that you do not gouge too deeply into any one spot on your rims.
Once your rims have been thoroughly sanded to an even brightness, rinse them with water and then polish them with aluminum brightener available to your local auto parts dealer. Wax your rims with a clear car wax to prevent further oxidation.