I have some old magnesium valve covers i would like to paint silver. I need it to be durable and heat resistant but dont want to spend hundreds on the project, its not a trailer queen. Have any of you guys painted magnesium?
This^^^ I had a set of magnesium covers done in the ‘80’s, had them on my coupe and then later on a GMC. They eventually started to blister and peel, I thought it was a poor coating job, never suspected outgassing.
While you definitely can anodize magnesium, it does work so well on die-cast parts due to a small % of silicone used in the mix in the die casting process. The finish ends up being very uneven and blotchy.
Cerakote is already very thin, although as with any paint/chemical check out the safety data sheet and instructions before mixing anything. In my experience you need an immaculate finish surface before applying Cerakote to get a good result (I guess same with any painted finish.) The Cerakote is normally such a thin layer it shows irregularities reeeaaaaal easy.
Cerakote Air Cure can be sprayed right out of the bottle through a paint gun, it dries like paint, and is superior to pretty much any paint or powdercoat. It can withstand glowing red hot exhaust temperatures and is oil resistant. The surface you're coating must be clean and free of any contaminates prior to coating. https://www.cerakote.com/shop/cerakote-coating?finishes=cera_c_series
To my mind, I'd be concerned with the value of the parts. Mag is rarely a cheap common part (VW cases being the exception). So whatever I put on, I'd want to be able to remove safely too, so I didn't ruin the value. Whatever coating I considered, I'd also check on removing it from magnesium. As mentioned, it requires require safe handling and can react very differently than other materials. If cast it's porous, which means you probably don't want to slather stripper on it either. I wouldn't abrasive blast it either.
I bought my covers at a swap in late ‘83 or early ‘84, the seller had a stack of raw ones, never painted. I didn’t ask how he acquired them but I thought they were unique and had the PCV holes I wanted. Initially I polished them and the first humid day they pretty much reverted to looking how I got them. Not my photo, I found this online. They were introduced on the ‘84 Corvette.
I called Cerakote like you guys recommended and while they claim it works on magnesium, ts $40 oz plus shipping. My model badger airbrush hold 4oz. It would cost a fortune to coat a car part.
Just some technical info: Dow 7 is just a chromate conversion coating. It has the Hexavalent chromium, which is now considered carcinogenic. That doesn't mean you can't use it. It's the same chromate coating as you might have heard called "Gold Cadmium". The Dow 7 or similar chromate coatings result in a yellow to dull yellow appearance. Note that trivalent chromium is what you commonly find on hardware store zinc plated parts. It is clear or slight blue tint. No mistaking it for the hex chromate, which is yellow or to even near olive drab green color. Basically what the conversion coating does is lower the galvanic potential of the surface, as you know magnesium is very active on the galvanic scale (more anodic officially). So by lowering the surface potential, you can delay the onset of the oxidation.
I recently rebuilt a VW engine with a magnesium case. I glass beaded the block and painted it with ENDURA urethane enamel. The rough beaded surface is great for adhesion. No primer just silver paint directly.
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