I really don't know, but from chem 101 that I took sometime after Moses died, I suspect that the Zinc from the Galvi will go first. You know the pecking order I'm sure. You use zinc tabs to sacrifice and protect the aluminum of a motor or hull. Alum should go to heck before the iron in the steele frame......but I can't remember much about the periodic table, I spent too much time looking at the girls.