Beryllium dust is pretty toxic. Also not cheap.Just based on numbers I quickly looked up (you want as close to 0V as possible to avoid corrosion):
The anodic index between Magnesium Alloy and Aluminum is about 0.8V.
The anodic index between Magnesium Alloy and Iron is about 1.0V.
Aluminium would be slightly better than the Steel/Iron hub, but it would still be very corrosive. Plastic would be best. Unfortunately, if you were bent on using metal, you best bet from a corrosion perspective would be beryllium . . .
Beryllium dust is pretty toxic. Also not cheap.
Vibration and shudder solved with the repair of 2 rims. Happy.
I am planning to have them powdercoated in this winter. Will that do?