Here are possible solutions:
"If your wheels are not clear coated, or the original coating is worn away or damaged, you can clean the wheels with "mag wheel polish" or fine steel wool to remove surface oxide and dirt (and what's left of the old finish) -- then repaint the wheels with a durable clear coat epoxy or paint designed for this purpose.
Unprotected aluminum wheels quickly corrode and pit when exposed to road salt and excessive moisture. If the corrosion continues unchecked for too long, the cosmetic damage may be too great to reverse. So if you don't want to drive around with ugly, pitted alloy wheels, use some type of coating (wax, sealer and/or paint) to protect them from the elements. "
From
here.