The wonderful thing about forums such as this one, is that you can do a search for topics previously covered. The harsh reality is that quite often, people stop coming to forums. So your new post may go unanswered if no one with experience is still around. That's one of the many reasons why it's good to search first. Plus, you may read something that you would'nt have asked, and therefore learn more than you intended to.
Here's two links to this same topic.
magnesium whell
Has anyone Powdercoated Magnesium?
I hope this helps. And if you have further questions, I'd suggest (i'm not demanding
) replying to one of the links i gave so that the topic of magnesium stays in one or two threads, rather than getting spread out all over the forums.