Aluminum panels are common in a lot of vehicles. They corrode just like steel panels but seem to not develop holes as easy. The aluminum corrosion is aluminum oxide which can protect the metal from further corrosion. It is the same as an aluminum light pole in the parking lot forming a protective layer. A bare steel pole would continue to corrode until it fell apart.
Steel and aluminum together cause galvanic corrosion. With dissimilar metals in contact and the presence of moisture, the lesser metal is sacrificed. Just like the magnesium anode in a fire truck or water heater, they are sacrificed to protect the tank. In collision repair we are diligent about isolating the two metal to prevent direct contact. The OEM's are great at it in some areas , in others they don't seem to care.
Aluminum is painted about the same as a steel panel. REmove all corrosion, prime, block, seal , paint.