Restoring Real Mag Wheels by Painting, Plating, Chromating or Clearcoating

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A. Real magnesium wheels are no longer produced in great numbers for the reason stated. Most mag wheels still in existence are on early street rods or nostalgia race cars seeing limited use. They have always been a high maintenance item with most early race teams letting the wheels return to their natural dark grey state after giving up on the tedious polishing.

A two-component urethane coating would likely hold up fairly well with a reasonably good appearance; however, I have leaned toward the use of a good quality lacquer for several reasons. While this coating will not hold up as long, it will look much better at thin films, can be easily waxed with auto wax, and ultimately can be easily stripped off with lacquer thinner ⇦[this on eBay or Amazon affil links] when the time comes for the inevitable re restoration several years later. A final thought is to be very careful when power buffing magnesium. Very few shops are set up properly to avoid the potential fire hazards when magnesium dust is present. Good luck!

A. Your flaking paint is most likely caused by improper cleaning of the magnesium prior to paint. Most painters that prep aluminum use the same low alkaline wash for Magnesium alloys. Magnesium alloys (with the exception of ZK60A) are not attacked by strong alkalies. After a warm water rinse, use a phosphate solution that will inhibit corrosion and improve the adhesion and durability of the finished surface. Use a warm water rinse and then chromate or dichromate the surface depending on the application. The chromate can etch machine surfaces to 60 rms or more but does create an excellent surface prep for paint.

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A. I am a paint manufacturer of over 20 years. Use a good Etching Primer. Use a finishing coat that will resist the range of chemicals in which the painted surfaces are likely to get in contact with. The success rate is 99%

? Are you talking about magnesium parts that are die cast or thixomolded? We've had issues with thixomolding and have resorted to a prime coat of Tagnite to improve paint adhesion.

A. Hi, Tony.

Please look in your yellow pages for "Plating Supplies", or in our Chemicals Directory here for those chemicals. But there is a lot more to chromating a magnesium wheel than dipping it into a vat of chromating solution. Read on and, just below, we will refer to some pages here that we've prepared specifically for chromating and other anti-corrosive treatments for magnesium.

But there is environmental liability for proper disposal of hexavalent chrome and its rinse water as hazardous waste (it made Erin Brockovich a household name). So you might be better off finding a Jobshop to do this project for you. Best of luck!

A. We do aluminum & magnesium finishing.

For chromating magnesium we use a product called Iridite #15.

You do not want to do this yourself. You would need all the other chemicals like mag soap, etc.

A. What type of magnesium wheels are they? Are they BBS? And why chrome? Chrome on mags sure wouldn't look good. Johnny nova Hi, Johnny. This isn't bright and shiny chrome plating, but a corrosion protection treatment called chromate conversion coating. Regards, Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey

"Magnesium Finishing"
by Dow Chemical Co.

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A. Hello Leonardo, hi Eddie --

Please see our quite comprehensive on-line article: "Finishing of Magnesium" by Tom Pullizzi which includes the needed info on the Dow #7 process / dichromating sealer, as well as thread 14207, "Dow #7 / Dichromate treatment".

If possible, also try to find a copy of Dow's "Magnesium Finishing" booklet (avail on eBay, June 2024) ⇨
Good luck.

Kellie,

A. A very interesting question! Perhaps pick up a copy of a magazine for performance cars, i.e., Hot Rod magazine. Many ads for magnesium wheels. Many manufacturers of this type. Contact them all.

Another thing would be to search the web with "magnesium wheels", see what turns up. Good luck!

A. I found this question in my ongoing search for a good way to protect my 16 x 13 Halibrand magnesium wheels. I've written some small articles that deal with the history of Halibrand Engineering and American Racing Equipment magnesium racing wheels. While far from being the definitive text on the subject, it's a start, http://roadsters.com/wheels/#Halibrand

Thanks for the link, Dave -- excellent article!

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Magnesium is very difficult to keep bright as you'll read above, which is why today's wheels are usually cast aluminum even if still called 'mag wheels'. Despite being difficult to polish, I think Mothers Mag & Aluminum Polish ⇦[this on eBay or Amazon affil links] is probably the best approach.
Best of luck.

A. Steve,

Quite a few people ask similar questions about aluminum and mag wheels.

Anyhow, I phoned up the local experts in Surrey.

They remove paint with paint remover BUT often use the Aircraft Stripper because often the paints (on good rims) are painted using a 2-component polyurethane paint.

They also shot peen if necessary. Then they apply a 2-component Polyurethane paint over the finished rims. They did it for us on a 7 year old car which showed signs of salt attack. Superb job.

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A. The problem is that magnesium is highly reactive and acid dipping (pickling) will not make it less so. You could clearcoat or lacquer the wheels, and it would help but not be a permanent solution unfortunately -- but if you can have a proper chromate pretreatment done first it might work.

Waxing is not totally labor-free but is a lot easier than mechanical polishing, so I think frequent hand application of museum wax ⇨
would make for less frequent polishing.

A. The vast majority of "mag wheels" are actually aluminum alloy. Most commonly, for North American cars & light trucks, alloy A356 (strontium-modified) cast by the low-pressure die-casting (LPDC) process.
A356: Al 91.1-93.3(wt%), Cu max 0.2, Fe max 0.2, Mg 0.25-0.45, Mn max 0.1, Si 6.5-7.5, Ti max 0.2, Zn max 0.1, Other, each max 0.05, Other, total max 0.15.

Alcoa produces forged wheels of Al 6061-T6 (to my recollection), mostly for heavy trucks.
Al 6061: Al 95.8-98.6(wt.%), Cr 0.04-0.35, Cu 0.15-0.4, Fe max 0.7, Mg 0.8-1.2, Mn max 0.15, Si 0.4-0.8, Ti max 0.15, Zn max 0.25, Other, each max 0.05, Other, total max 0.15.

Magnesium wheels are usually die-cast, probably mostly by the high-pressure die-casting (HPDC) process. Quantities are small in comparison to aluminum. The alloys are given in ASTM B94 and are mostly variants of AM60 & AZ91. E.g.,
AM60A: 5.5-6.5% Al, 0.13% Mn min,0.50% Si max, 0.35% Cu max, 0.22% Zn max, 0.03% Ni max, balance Mg.

AZ91D: 8.3-9.7% Al, 0.15% Mn min, 0.35-1.0% Zn, 0.10% Si max, 0.005% Fe max, 0.030% Cu max, 0.002% Ni max, 0.02% max. other (each), balance Mg.

Also, a UK site mentioned an RZ5 alloy used for wheels in both Formula One and Superbike competitions.
RZ5: Mg 94.05, Zn 5.62, Zr 0.19, Ce 0.10, Nd 0.03 (wt%).

Now, please explain 'Dietz number' and its relevance to magnesium, finishing and welding; I suspect it's not the kerosene lanterns & Wyoming coal mines found by googling.

"Magnesium Finishing"
by Dow Chemical Co.

is sometimes available on
AbeBooks,
eBay, or
Amazon

... but if not, you can find libraries which have copies on WorldCat.org

(affil links)

A. Hi, Bruce. We have an article online here that explains the various approaches to magnesium finishing: "Finishing of Magnesium".

Dow's "Magnesium Finishing" handbook is a great reference ⇨
but it is out of print and hard to find.

Good luck.

Regards,

A. Yes, magnesium can be chrome plated. It may take some effort to find a shop which does that as the demand must be very small.

I can't say for certain, but the highly reflective wheels in your second photo, I'd wager are highly polished and buffed magnesium and are not chrome plated. They may have a clear lacquer coat to keep them shiny longer.

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  Yes the wheels in the second photo were highly polished and would stay like that as long as they were attended to with Mothers Mag & Aluminum Polish ⇦[this on eBay or Amazon affil links] or White Diamond metal polish ⇦[this on eBay or Amazon] .

I also had success with a product called Sharkhide ⇨
which is used as sealant coat for aluminum pontoon boats. But to be fully sealed the wheels would have to be polished, then fully sprayed with Sharkhide so no areas were left exposed. That means the wheels need to be unmounted. The coating acts as a clear sealant and a buffer to the environment. I did a test on a polished magnesium timing plate starting from a gray color and after polishing and sealing, it was left untouched in the environment for a month. It was rained on it plenty of times. The uncoated portion grayed up and the rest remained polished.

A. Hi Markus. It is true that chromate conversion treatment with hexavalent chrome, like the examples you mentioned, can be a good preparation process, however, chromates specifically tailored for magnesium would be better than what you mentioned which are tailored for aluminum. Due to RoHS and other toxic reduction programs, you may not be able to buy or do such hexavalent chromating these days. Not quite as good, but still worthwhile, might be a trivalent chromate conversion coating such as Alodine 5200 (I don't know for sure, but I suspect there may not be any trivalent chromates designed for magnesium).

Regards,

A. Try phosphate finish. According to Russian sources you can use 0,3 gm sodium silicium fluoride/ 30 gm manganese monophosphate/1 lit water solution/ temp. of solution 95-98 °C/15-20 minutes immersion. Hope it helps and good luck

A. Hi Markus. As you can see on this page, Dow wrote a whole book on the surface treatment of magnesium. Finishing.com's Tom Pullizzi wrote a fairly complete summary of magnesium treatments back in 2000.

But in short, the products you mentioned are fairly similar non-chromated products from two major suppliers, and either should be okay. It is true that it gets harder and harder to get small packages of such products, but you might inquire of a local distributor of such metal finishing products.

Luck & Regards,

A. Hi Markus. Even though you stripped and glass blasted the rims, that was a while ago, and magnesium is a very active metal which oxidizes a bit immediately, but additionally as time goes by. The other forum was apparently suggesting a pretreatment in Alumiprep 33 (now apparently renamed BONDERITE C-IC 33) ⇦[this on eBay or Amazon affil links] , which is a phosphoric acid based cleaner/pretreatment for aluminum, perhaps on the basis that the acids in the Bonderite M-CR 1201 (probably formerly called Alodine 1201 ⇦[this on eBay or Amazon affil links] ) may not be reliably strong enough to dissolve that oxidation depending on the time elapsed since blasting, etc.

It is difficult to proceed with book learning or internet learning to processing a set of rare magnesium wheels when that metal's traditional finishing steward (Dow Chemical) decided to abandon the field, leaving us with only "magnesium is sort of like aluminum in some ways, so the chemicals designed for aluminum processing will have to be tried", and because the supplier of those chemicals is a multi-billion dollar megacorp uninterested in selling an individual a small quantity nor in their success in treating their rare magnesium wheels with this product designed for aerospace aluminum.

Moreover, it is also generally understood that "your mileage may vary". So at this point I would suggest that you try to chromate treat (Bonderite M-CR 1201) some scrap magnesium of the same grade as your wheels if you have any available; and if not, then bite the bullet and treat ONE of your set of wheels and paint it, then see what you learn from actually doing it. If it looks good, and you can't pull any chips of paint off with duct tape, proceed with the others.

Apologies that perfect instructions are unlikely to be forthcoming in an age where old magnesium wheels get ever rarer, formerly available products are no longer made for environmental reasons, multi-billion dollar megacorps have bought up all the old small suppliers, then dropped support at the drop of a hat. Sorry about what happened to the magnesium finishing industry, but there are still jobshops specializing in finishing of magnesium, and you might want to rely on them rather than doing it yourself.

Luck & Regards,