Coating/restoring real mag wheels

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.

  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 [on eBay or Amazon] or White Diamond metal polish [linked by editor to info on Amazon].

I also had success with a product called [on eBay or Amazon] 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. 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 [on eBay or Amazon] 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. Hello Leonardo, 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 letter 14207, "Dow #7 / Dichromate treatment".

If possible, also try to find a copy of Dow's "Magnesium Finishing" booklet .

You may also want to see our "Introduction to Chrome Plating" if chrome plating is one of the options you want to consider. Good luck.

Kellie,

A. A very interesting question! Perhaps pick up a copy of a magazine for performance cars, i.e. , Hot Rod Magazine [affil link to Amazon]. 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,

A. Magnesium is very difficult to keep bright as you'll read above, which is why real mag wheels are rarely sold anymore (today's wheels are usually cast aluminum even if still called 'mag wheels'). Despite being difficult to polish, I think Mothers Mag & Aluminum Polish [on eBay or Amazon] 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.

A. The problem is that magnesium is highly reactive and acid dipping (pickling) will not make it less so. You would need to either clearcoat or lacquer the wheels, and neither is a permanent solution unfortunately.

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.