In order to clean aluminum that is not painted, mix a small amount of mild detergent with warm water. Apply with a clean washcloth or sponge. For the detergent, use something along the lines of dishwashing liquid. Many liquid hand soaps will also work fine for this type of cleaning job.
Generally, it is not a good idea to use abrasive pads or cleaners on aluminum, as the metal will scratch easily. If you must clean aluminum using some type of abrasive, try applying baking soda to the surface and then rubbing with a moist cloth. This will work as well as most scouring pads and is less likely to create deep scratches on the surface.