Funny this comes up today. I just bought a few cans of Tempo zinc chromate spray primer to use in refinishing magnesium rims from my Alfa spider. A plater I spoke with told me the only way to prevent the mag from reacting with 02 is zinc chromate--paint and even powder coating will not truly seal the metal, so oxidation occurs regardless of finish if this treatment is not used. Having sprayed these rims a year ago, and seen the disaster that ensued, I can believe it.
Not too related to the frame issue, but for what it's worth.........
Cheers,
