Magnesium forms an oxide layer, similar but stronger, to aluminum metal. It creates a dull, white layer. This protects the metal from further decay. The reason steel rusting is so severe is that iron oxide expands to around 10x its original size and flakes off. The oxides of aluminum and magnesium stick tightly to the metal, and form a protective layer that pervents further rusting.

W/O a coating, magnesium parts will be okay. Now, if you want to keep it shiny, then a coating will be necessary. Unfortunately, I have no experience in painting magnesium parts, so I cannot suggest a best course.

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2010 Toyota matrix

'93 500 SEL
Well, I sold it. Just got to be too much to keep up with.
First time I haven't owned a MB since 1983.

'12 Volvo S80 T6
Needed something that wasn't as hard to deal with as my bad addiction

'18 Mazda Miata
No more boring cars for everyday transport!