Real MAG(nesium) wheels restoration.
Real MAG(nesium) wheels restoration.
(OP)
The reasons for my questions are I plan to refinish 40 year old magnesium wheels for a car restoration.
Believe it or not, but the internet wheel restoration from various sources differ from each other and from the few engineering references. Thus I don’t have a clear idea what is needed.
The primary myth from the car experts is that magnesium ages and must be relieved by heating to “around 300F” for “about an hour” and then cooled “slowly”. The quotes are due to no exact information as rate of heat up, true hold and cool down rate. My limited search of engineering material implies that a 300F heat soak is to actual accelerated the age harden of magnesium.
Another reason for the 300F heat soak is to expel corrosion related gases that will seep from a freshly painted wheel.
There is a local weld shop that has an oven for powder coating I would try to use.
So the first question, is there a need to heat treat a 40 year old magnums wheel and if so the recommended rates and temps.
Next question is about the surface treatment to prevent corrosion. The wheels current retain 90% of the original paint which I have been told is over a special magnesium primer. One recommendation is not to completely remove this finish, just lightly blast away the “burnt paint” following heat soak and then apply a zinc chromic primer. I have also read about various “Dow” pre treatments of which seem to be a solution of chromic acid, plaster of Paris and water applied for a few minutes, then thoroughly washed off and dried prior to priming.
The Dow solutions seem restricted or just not available. Even chromic acid seems difficult to obtain. I THINK I could get a 10% solution.
So the next question is mainly to provide the instructions for using a chromic acid wash, even recommendations about which primer would be great.
Thanks
Believe it or not, but the internet wheel restoration from various sources differ from each other and from the few engineering references. Thus I don’t have a clear idea what is needed.
The primary myth from the car experts is that magnesium ages and must be relieved by heating to “around 300F” for “about an hour” and then cooled “slowly”. The quotes are due to no exact information as rate of heat up, true hold and cool down rate. My limited search of engineering material implies that a 300F heat soak is to actual accelerated the age harden of magnesium.
Another reason for the 300F heat soak is to expel corrosion related gases that will seep from a freshly painted wheel.
There is a local weld shop that has an oven for powder coating I would try to use.
So the first question, is there a need to heat treat a 40 year old magnums wheel and if so the recommended rates and temps.
Next question is about the surface treatment to prevent corrosion. The wheels current retain 90% of the original paint which I have been told is over a special magnesium primer. One recommendation is not to completely remove this finish, just lightly blast away the “burnt paint” following heat soak and then apply a zinc chromic primer. I have also read about various “Dow” pre treatments of which seem to be a solution of chromic acid, plaster of Paris and water applied for a few minutes, then thoroughly washed off and dried prior to priming.
The Dow solutions seem restricted or just not available. Even chromic acid seems difficult to obtain. I THINK I could get a 10% solution.
So the next question is mainly to provide the instructions for using a chromic acid wash, even recommendations about which primer would be great.
Thanks





RE: Real MAG(nesium) wheels restoration.
I would also suggest not using chromic acid as legal disposal will be very difficult.
Considering the poor ductility and fatigue properties of Mg I would suggest removing all of the paint and having dye penetrant inspection done to assure that there are no cracks.
There are special paint systems for Mg. I would think that any of the big coating (don't call it paint to their face) suppliers could give you a compatible primer/top coat system.
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P.E. Metallurgy, Plymouth Tube
RE: Real MAG(nesium) wheels restoration.
But quite frankly, magnesium alloy rims is a job for specialists.
I'd take them to someone who does classic car wheels on a daily basis.
OK, I'm a chicken
RE: Real MAG(nesium) wheels restoration.
I knew a guy with an '57 Vette. He got a hold of a set of wheels that were cast Mg.
Around the outside edge they cast in the words "Property of Kelsey Hayes Inc Experimental not for street use" or something to that effect.
He paid a pro to clean them, check for cracks, and refinish them.
There were suspect spots in a couple of them, they went on the rear.
Guys at K-H found out and tried to buy them from him, these were the only ones from the test days that existed.
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P.E. Metallurgy, Plymouth Tube
RE: Real MAG(nesium) wheels restoration.
I don't know what to suggest about the heat treat advice, it sounds wrong. Work hardening is precisely what you do want in a soft metal. perhaps they are trying to regain the temper and ductility of the softer base metal, but my experience with aluminium wheels is that heat treated to higher hardness is better than running with no heat treat. At work we were quite specifically banned from running gravity cast un heat treated aluminium wheels on public roads. Oddly that describes >>50% of aftermarket wheels.
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Real MAG(nesium) wheels restoration.
Mike Halloran
Pembroke Pines, FL, USA