Cracked alloy

[oscarisapc]

Has anyone seen this problem before? I have recently acquired a MY55 W203 estate which was reported during my first service service of it to have a cracked wheel on the inner rim.
(see pic)
There is no other sign of damage to the wheel or suspension - is this just something that happens from time to time or should I be looking for other signs of a hard knock? The car had sone 55k miles as a company car before I bought it - it had been serviced properly but not really loved.

I guess this wheel is fit only for scrap. Has anyone got a spare W203 Elegance 17 inch 7 hole wheel? The part number is A2034013202.

 

[lynall]

Me personally i would have that tig welded up and back on the car, but thats defo a personal thing.



Lynall

 

[talbir]

Yes, you can have an alu welder sort that out no problem.

I have had cracked wheels and had them alu-welded up and back on my car without any issue....scientifically, the point of weld is stronger than the rest of the wheel !

Defo check the suspension for any signs of a hard knock, but these cracks do occur without a hard incident, sometimes just the combination of angle and pressure is enough without the speed.


cheers
talbir

 

[stumpy1]

Had the same on a Bentley wheel. Was advised that it can be welded but decided to fork out for a new wheel just to be sure of no further issue. Our roads are so bad that it doesn't take much to kill a wheel. If the tyre is ok, I'd just get your tracking checked. Mine was knocked out therefore scrubbing the fronts in no time.

 

[EDZ649]

For peace of mind..........get a new wheel.

 

[geoffd]

cracked rim

I'd have thought that sort of damage is typical of having taken one of those square road humps a mite too fast. That puts an unequal load on the relatively unsupported inner edge of a wide rim.

If it was me, given that one has been damaged, I'd be tempted to have the other three crack tested. After all whoever did it might have made a habit of flying from hump to hump. And I definitely wouldn't be welding up the crack - my life is worth more than any alloy wheel !

Geoff

 

[talbir]

And I definitely wouldn't be welding up the crack - my life is worth more than any alloy wheel !

Geoff

Scientific fact - the point of weld has a greater tensile strength than the rest of the metal.

So no weakness at all in a cracked alloy that is corectly repaired with alu-weld.

talbir

 

[oscarisapc]

I think I will get a new one

The crack was discovered by MB Nottingham when they did a service as part of their free safety inspection. It was good that it was spotted. It would have been easy for a busy technician to have overlooked it. I think that any other cracks would also have been noticed at the same time. I had all the wheels off because the entire brake system (discs and pads - front and back) was being renewed. I haven't taken the other wheels off to inspect personally but will be looking very closely when I get new tyres.

I still haven't managed to source a replacement wheel - does anyone know where I might get one at less than the £200 plus that the dealer is asking? I have tried asking some of the folk who post on this forum and are in the business but they don't respond.

I can't argue with the science that a weld is stronger than the surrounding metal. However, with wheels I am not at all sure that the tensions within the metal would be properly dissipated and unless the person I asked really knew what they were doing (how can you, as a punter, know that?) I am going to err on the side of caution and get a new one.

 

[jaymanek]

have you tried euromerc?

 

[oscarisapc]

Thanks. Yes I have - no response to several emails and there does not seem to be a phone number.

 

[Howard]

Nicks been round at mine all evening , he'll get back to you don't worry ....

 

[geoffd]

re welding cracks

I have no argument with the fact that a weld may be stronger than the base metal.

I do have some experience with welding cracks - not on wheels but of industrial equipment subject to vibration, and the problem with welding cracks is knowing where to start and stop. To ensure that the crack can't further propagate, the end of the crack needs to be drilled to dissipate the crack stresses, then the whole thing welded up. The clever bit is knowing where to drill because it's not always obvious where the end of the crack is without testing with dye penetrant or similar technique.

So while the weld may be strong, if the crack can still propagate, the repair won't be safe. And that's why I wouldn't take the risk with a wheel.

Geoff

 

[oscarisapc]

end of story

I finally got a replacement wheel. None of the UK suppliers who I contacted by phone or email ever got back to me. In the end, after an internet search, I got a wheel directly from Germany from a very helpful outfit called 321autoteile
321autoteile
I have no connection to the firm so this is by way of a recommendation rather than advertisement. They communicated in English (always a help as I don't speak German) and were true to their word - a replacement wheel arrived within a couple of days of ordering. After exchange rates and carriage are taken into account it cost me £108.45 which is less than half the UK dealer price. I would deal with them again.

I have taken more photos of the crack in my wheel - sufficiently scary that I have posted them on the main forum as it seems there is a big safety lesson there in terms of cracks being bigger than they appear.

 

[hotrodder]

Scientific fact - the point of weld has a greater tensile strength than the rest of the metal.

So no weakness at all in a cracked alloy that is corectly repaired with alu-weld.

talbir

It's a bit more complicated than that, especially when talking about aluminium.

Every weld will have a HAZ (heat affected zone) where the grain structure of the base metal has been altered due to the heating/cooling. Depending on the alloy being welded this HAZ can become harder and more brittle than the rest of the base metal (excessive cooling rates in carbon steels), have an effect on corrosion resistance and strength (stainless alloys) or become softer and weaker (ALL aluminium alloys regardless of skill/technique!)

Welding aluminium will always result in softening of the HAZ effectively annealing or at least partially annealing an area adjacent to the weld. If the alloy being welded was already annealed then no big deal but many of the alloys used for car wheels are heat treated to strengthen them. Cheaper (heavier) wheels cast from a non heat treatable alloy will certainly not be annealed and thus locally softened by welding

Obviously have no idea of the alloy or temper used for the wheel in the OP but some common alloys for cast wheels include A356-T6 and A365, forged/spun wheels are made from 5454, 6060-T6, 6061-T6 and no doubt others too

To put some numbers out there... 6061-T6 has a UTS of around 45ksi, anneal it (6061-O) and the UTS is circa 18ksi. Yield for 6061-O is only around 8ksi!

About the best you can expect from a good weld (welder knows what they're doing and doesn't dither around pouring heat into the wheel) on 6061-T6 is a UTS around the mid 20ksi mark.

The effect on strength with cast wheels is a little less (welding is casting, the act of forging a wheel refines grain structure adding strength) but castings are generally more fussy- porosity and inclusions to deal with making the welding more difficult and prone to faults

 

[ringway]

Without question, a new wheel would be the only option for me.

 

[talbir]

New wheels work if the wheel is in current production but some of the older AMG / Brabus collector cars have wheels that are no longer in production. So only option is to either have the crack repaired or loose the originality of the vehicle.

I have a 3-piece AMG rim that had a crack, has been welded and used by me on my car for 4 years since the weld....with zero issue. The car is a 5.6 litre 340 bhp car with a 2.82 rear end (the wheel is on the rear) ...so under highest stresses it has not failed.



talbir

 

[hotrodder]

Wheels (like pretty much everything) are designed with a safety margin, they're 'overbuilt' so the loss of strength/hardness from welding doesn't automatically make them unsafe however there are lots of ifs and buts...

Cheaper/heavier wheels are cast from a pretty simple alloy and are relying on the sheer amount of material in them for strength. Welding will have less of an impact on this type than for a lightweight forged and heat treated wheel that uses design, grain structure and heat treatments to engineer the weight out

I know where you're coming from regarding old/rare wheels. I've got a set of early 911 Fuchs, took me a couple of years to find a replacement wheel in good condition at sensible money

Something to bear in mind with aluminium in general, it has no endurance (fatigue) limit. Unlike steel or titanium aluminium parts cannot be designed to last indefinately.

 

[Barryh]

I have had this twice now and replaced the wheel both times ,partly safety and partly no time to run around on space saver.

Next time I will try the German option.Are you sure they were genuine MB wheels at that price?

 

[oscarisapc]

Germany supplied wheels

Genuine wheels with an MB logo and part number - they are pre used but so are all three other wheels on my car. I would have been in the market for a new or second hand wheel supplied in the Uk but, as I mentioned earlier, I did not get any reply to my queries. I didn't try the suppliers who only deal in sets of four. I Googled in the part number which gave lots of hits in German. However, a large number of German sites also have English versions. My daughter speaks the language so I knew I could get myself out of a hole if I needed to phone up, but in the event everything was painless and conducted by email in English.

 

[johnsco]

I agree with most of hotrodder's comments.
I've spent a fair amount of time dye-penetrant testing welds in aluminium fabrications ... Not always with satisfactory results.

Point No 1. For every 100 good welders in steel, you will find one or two who are good welders in aluminium.
Point No 2. The weld metal may or may not be stronger than the parent metal, but the heat-affected zone will certainly be modified by the welding process and will, in every case, be less strong than before.
Point No 3. Certain aluminium alloys (and there are very many) are not very suitable for weld repairs, even by good welders. Some suffer from conditions known as "hot-shortness", which then tend to be susceptible to cracking in the heat-affected zone.

To do a proper weld-repair, the welding engineer would need to know the alloy composition of the wheel.
He would then need to use a technique taking into account the correct grade of welding consumables to use, any pre-heating requirements prior to welding and any subsequent post-welding heat treatment.

Following that, and a dye penetrant crack test after a day or two, I might trust my life to it.

Sorry to be so cautious.
When I get my job badly-wrong, you'll all hear about it.

Cheers.
Johnsco