One other thing that will help, is to apply a sacrificial anode to the corroding metal (the aluminum part). If you were to rivet a block of magnesium to the aluminum, it will in turn absorb the currents causing corrosion and it will corrode instead of the aluminum. I used to work for a gas company monitoring the sacrificial anodes (bags of magnesium chips) that were electrically connected to all the steel pipe in the ground for the same purpose. They also do the same thing for outboard motors - look at the foot of the drive, you will see a small block of sacrificial magnesium bolted to the motor to prevent the corrosion of the motor and drive.