NDT of magnesium wheels?

[911hillclimber]

The site I would normally ask this tech question on has closed down, but though someone in the membership might have some advice for me please.

I have real DYMAG magnesium wheels on my race Lola-Porsche.
I have noticed a suspicious long 'defect' line in one of the rims yesterday and suspect it may be a hairline crack.
It is 70mm long and axial to the drive shaft, ie at 90 deg to rotation of the wheel.

The wheel holds air well.

I want to crack test this area asap as the next meeting is 3 weeks away.

Has anyone used some dye penetrate or similar to confirm or otherwise this could indeed be a crack on FUCH or similar wheels?

The wheels were last tested 10 years ago locally, but that Lab has since been closed.

It's the one on the left.

[911hillclimber]

Resolved!

[Cortina]

Yes - have dye pen tested a cylinder head (lotus ?) . More practical than MPI for obvious reasons .... for the DIYer. This was a fair time ago - guessing you can still get "the stuff" , but with all the health and safety crap about ... who knows ??? I would have thought the paint needs to come off ?

[Cortina]

how ?

[911hillclimber]

Too simple for now!
We have some events coming thick n fast in 3 weeks time, so i needed to find if this is the start of a catastrophic failure or what. Lines like these don't arrive for no reason.
My next event is Shelsley Walsh, and a wheel failure at 104 mph would not end well..

A long time ago I had another set of rims for the car, all stored in the attic of the garage and found them this afternoon. They fit the car, are dimensionaly the same as the current wheels, and one of the pair is arrow straight and rings like a church bell, crude test but the casting I think is good.
So:

Going to have the AVON slick removed off the 'cracked' rim and mounted onto the one I have in the attic.
That fixes my immediate problem of having a good known wheel for the coming events in time.

With the tyre off, I can get the 'cracked' wheel NDT locally, have contacted 2 companies, and if scrap then that is that, but the car is safe. Welding old mag wheels seems a poor solution tbh.

These old magnesium cast wheels are almost never used today on track due to cracks, so really on borrowed time.

Modern replacements are very expensive and just might have to bite the bullet, probably with Image Wheels just down the road from me. At least I only need 2.(about £1000 bill)

[RobFrost]

I would weld the wheel. Or have it welded. Especially if you can find out the alloy it is made with.

I was looking into the metallurgy of magnesium. It hardens over time and eventually becomes brittle, but if you bake it, it becomes less brittle again, exactly the same way you reduce the temper of quench-hardened carbon steel by baking it.

The people I asked thought that if you preheat it, weld with AZ92A filler rod, then bake out the welding stresses, it is a strong repair. What welding will not do, however, is have the strength of forged metal. Only cast.

AZ92A is suitable for almost all magnesium alloys and you can use AZ63 too.

Its other weakness is becoming porous through corrosion, but I doubt that has happened to your wheels, being well coated and stored indoors.

I also totally understand you wanting new wheels rather than risking your life on a repaired old wheel.

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[911hillclimber]

Thanks Rob, most helpful, and a topic on your mind.
I need to fix the car quickly, and finding welders etc who will do this is hard, and bound to be in Essex or Scotland as it usually the way things pan-out for me!

I have found a local NDT company by me, ScanTech in Brierley Hill, but they have not quoted yet...

It was expensive 10 years ago when the wheels were last tested.

This line has appeared since i last removed and cleaned them after a meeting, so in just 6 miles of hillclimbing it has appeared.

Sets my engineering alarm bells off. Other side is ok in that i can't see any cracks.

Shame really as the wheels are so very very light.

[Lightweight_911]

.

Surely if one of the wheels is 'suspect' it would be sensible to get all 4 current wheels crack-tested ?

There are very few people I would trust to repair a damaged magnesium wheel - especially wheels from a competition car - Ian Jemison (who I'm sure you're already aware of) would be my first choice ...

.

[deano]

Lots of DIY NDT spray kits available cheap as chips e.g. https://www.weldingsuppliesdirect.co.uk ... 400ml.html

[911hillclimber]

Slick cross ply now on the other rim and (eventually) balanced, I think...
Fitter had a lot of trouble getting the wheel on the balancing machine and running true.

At Shelsley, BMTR will be there, and if it is out of balance, I'll have them correct it.

The other wheel to the one now in use was repaired/straightened by Jamison after a big OFF at Loton in my early days with the car.
I think he is the only place i would send the wheel to be welded, however...

With the 'cracked' rim free of it's huge tyre, it can he held like a bell and tapped with a screw driver: certainly rings out and for ever.

The good rim rings at a higher pitch and for longer, not exactly a real test!

I rubbed the 'crack' down to the metal, ite all the paint off 10 mm either side, and i have to admit, not sure it is cracked!

No marks on the inside face so if a crack has not gone through yet to let air escape.

Only way to check is to test properly.

The ebay kits are all well and good as long as you can interpret the result; easy to kid yourself by an ignorant look-see approach.

[RobFrost]

Sounds like it's just a scratch, Graham. Better safe than sorry, though.

[911hillclimber]

Took the wheel to ScanTech who are 30 mins away for a professional test.

We cleaned the 'cracked' area of any paint and undercoat down to the magnesium surface, about 50mm either side of the line, cleaned it very thoroughly and applied the penetrating agent, a light rose colour.
It needs 30 mins to get into any imperfections.
So time past by and the dye was cleaned away and the 'fixer' sprayed onto the treated surface.

If a crack etc was there it will now show clearly.

Nothing came up, area clean as a whistle, so all ok with the wheel.

If the casting had been 10 mm or so thick he would have used ultrasonics, but at this thickness, about 6mm, this is a good approach.

So, an exercise in safe not sorry. Total cost £90 and I've learnt a bit and even remembered some details from my past.

[RobFrost]

Good result. Better safe than sorry.

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[911hillclimber]

Indeed Rob, It was just a scratch but the feel and look of it was not normal in my eyes, but all done now.

These Dymag wheels with no cracks and no corrosion are very very rare, and a pair are worth more than £1000