Will bare magnesium corrode?

Through trying to acquire enough parts to build a 75 Yam MX400B, I somehow acquired enough parts to almost build three of them. Not sure how that happens, but I am hoping some of you can relate. Some of the parts are not nice enough to include on a race bike or restoration, but they would function. I am hoping to take that pile of parts and build a bike with a modern color scheme. I would like to paint the tank Yam blue and leave the engine and hubs bare, but I worry about the magnesium parts corroding. I have already discovered that the inside of the ignition covers corrode when left bare so I am sure the insides would need to be painted, but I am thinking the outside would be fine since I pressure wash and blow off my bikes after each ride. It seems to me that magnesium must be exposed to moisture for a while before it starts to corrode. I believe the inside of my ignition cover got wet from the pressure washer which led to the corrosion. I have had bare magnesium engine covers sitting in a plastic bin for over a hear with no corrosion, so it seems that moisture in the air does not cause corrosion. Does anyone have any experience with bare magnesium?