BBS Racing Magnesium Center Metallurgy?

[MotoSook]

Anyone know what the alloy is? I doubt it's pure magnesium. So! Anyone know the alloy?

TIA,

[javadog]

Souk;

You don't mention what wheel, or why you need to know. Are we talking 30 year old stuff leftover from a 935 or newer production?

In general, magnesium used for structural purposes is never pure. It is always alloyed with other metals, typically aluminum and zinc, plus other trace metals. The alloy is diiferent according to how it will be produced, heat treated, whether it will be machined, whether it needs to have greater fatigue strength, or strength at high temperatures or a dozen other things.

BBS has developed new ways to make wheels out of mag alloys. Some of the processes are new and they are now using many alloys they have developed and are "proprietary."

What are you after, specifically?

JR

[MotoSook]

JR:

I have 3-piece BBS Motorsports rims with magnesium centers. There are modern castings, as oppose to the the old 935 wheels.

Anyhow, I am going to powercoat the centers. As most alloys won't be structurally affected until prolonged exposure at 300+deg. C. I should be OK, right?

[javadog]

Well,

Let's forget the affect that the heat curing of the powder may have on the alloy and ask ourselves a different question. I have no idea what you will be using these wheels for but I hope it's not a street car.

In the good old days, race wheels needed to be inspected for fatigue cracks and corrosion at least once a year and more often if they got a lot of usage. To do this properly, the paint needs to come off. This suggests you want to use a paint that is easily stripped, which would rule out powder-coating. The other consideration is that a brittle paint ought to be used, so if a crack develops during the year, the paint might fracture and render the crack visible to the naked eye. Some paint films would remain intact over a new crack.

Cheap and nasty Krylon lacquer paint was the material of choice.

You may wish to contact the motorsport guys at BBS USA and get their views on the subject.

JR

[MotoSook]

Actually, powercoating will reveal stress cracking pretty well too. I believe some chassis fabricator powercoat tube chassis to aid in crack detection. Periodic dye penetration over the powdercoating should aid detection. If the epoxy coating is cracked, chances are the metal underneath may be cracked too.

I feel safe/comfortable enough to run the wheels on the street.

If I wasn't worried about the wheels looking like poop uncoated, I would strip them and run them raw. Anyone seen those wheels uncoated? Is the modern mag alloy more corrosion resistant?

[javadog]

I would never run a mag part uncoated. Vintage, modern or otherwise. I don't think you'll get anybody worth a damn to crack test a wheel casting with paint on it. Powder coating may crack but, if you have to remove it periodically, it's a bummer; not to mention that the removal process is not so good for the casting.

Talk to BBS and see what they say.

JR

[MotoSook]

JR - I would perform the NDT myself.

I agree about the need to coat...magnesium looks great bare...for about 2 mintues!

Maybe I'll just strip the centers and clear coat them. But with less durable paint (or clear) the coating may crack and the dye penetration test would be inconclusive. I don't have access to an x-ray machine.

Maybe I'll come up with a mag-flux test I can perform in my garage.

[javadog]

In your neck of the woods, I'd look for a company that crack tests stuff for the aircraft industry and talk to them. There ought to be a bunch of them up there. It's worth the money to do it right, if you're going to do it at all. It's important enough that when I used to send wheels back to the manufacturer for testing, they wouldn't even return any wheel that didn't pass, out of fear that I'd be tempted to fix it or use it.

Ultinmately, it's your butt on the line...not mine.

Good luck,
JR

[MotoSook]

I've got a couple of labs I use for testing. Cheers!