Aluminium Fatigue

Alan_uk

A2OC Donor
Just chilled out watching the Megastructures TV program on designing and building the QM2. Program said that they avoided aluminum for the upper structure, even though it would save substantial weight and consequently allow the ship to be within its target width. It had been used on the QE2 but now that ship was prematurely coming to the end of its life due to aluminium fatigue.

Quick google showed this on a bike site: "You should be aware that aluminium has a limited life - aluminium frames usually have a guarantee of five years maximum as they fatigue"

Maybe ships and planes are under more stress than A2s hitting pot holes!!

And there was me thinking I could keep the car for ever ;-)
(well more than 10 years)
 
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erstens

Member
What can be done by Audi to correct this fault?
Hi. I am "erstens" in the German forum.
Audi will offer a repair solution this year. All we know is, that they try out two different methods to repair.
We don't know for shure but one could be foarm (PU-foarm?) or something like that.
Or using a some sheet metal but what they did at someones car was mounting four new doors! But will the color match?

But I told you here: http://www.a2oc.net/forum/showthread.php?p=45080#post45080


In any way: I don't see any problem with the frame. It will be good for a real long time because it so stiff/
rigidly.
But there is a problem with the doors. But this is a constructive fault. There is to much movement..
 
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Skipton01

Well-Known Member
Hi. I am "erstens" in the German forum.
Audi will offer a repair solution this year. All we know is, that they try out two different methods to repair.
We don't know for shure but one could be foarm (PU-foarm?) or something like that.
Or using a some sheet metal but what thay did at someones car was mounting four new doors! But will the color match?

But I told you here: http://www.a2oc.net/forum/showthread.php?p=45080#post45080


In any way: I don't see any problem with the frame. It will be good for a rel long time because it so stiff/
rigidly.
But there is a problem with the doors. But this is a constructive fault. There is to much movement..
That is interesting and encouraging to read, as I've just checked Tanks doors and the splitting is happening on the front passenger door (right hand drive model, so this would be the drivers door on European versions).

This puzzles me as that particular door is used far less often than the driver door, which at the moment seems fine.

Cheers,

Mike
 

bill bell

Member
aluminium decay

This occurs onall vehicles since coach building began to use aluminium.

Unless anodised, it will always decay due to air pollution. Ships and planes suffer far more than any car for obvious reasons, the former salty sea, the latter constant use, 24/7.

I had a friend who had a 1930s Bentley Hooper bodied car, splendid car but after 60 years it did have some problems.

Still worried?? I don't think so !

bill bell
 

maersk

Member
Passenger door used less frequently - less lube, more friction in the hinge - door structure flexes slightly each time it is used = fatigue.

MTB frames in Alu are only gteed for 5 years but they do go on for ever - until they catastrophically snaparound the head tube/down tube interface.

As A2 does not have a head tube/down tube interface all should be well !!!!

Look forward to A2s little brother, the steel A1 in March next year !

Hope they galvanise it all like A4 and not just the bottom bits like A3.
 

Mark Brigg

Member
Corrosion, fatigue and tearing are all three seperate issues.

Re Alan's aluminium bicycle frame. There are many different alloy families with aluminium. Some years ago aluminium bicycle frames were made from 2000 series alloy and welded together. Its very well known in aluminium circles that the welding of 2000 and 7000 series (high strength as used in aircraft) is a big no no. Why? The welds corrode and your bicycle falls apart. Todays aluminium bicycles are fabricated from 5000 series or 6000 which both offer excellent corrosion resistance and safe welding. Some top of the range bikes used 7000 series but were bonded using adhesives. This top end of the market is now served by carbon fibre. By the way aircraft are riveted so Ryan Air is safe to use provided you don't need to take luggage or are disabled.

Re the door hinges. To be honest I haven't taken much notice here as my A2 is OK. The hinges are a 3 piece design. Where and how are they failing?

The spaceframe and other aluminium parts on our A2 have been generally well thought out by Audi who used many years of experience and experimentation in helping them reach the decisions they took, the A8 being a good example. The 6000 series alloy components (extrusions, sheetmetal and castings) Audi chose are safe. 6000 series alloys offers excellent corrosion resistance in normal conditions including marine and salt**ter environments. Galvanic corrosion, I'm again sure that Audi have taken good care of things, technology has moved on since 1947 and the corroded older Land Rover Defender tailgates we still see around. The liability of crash failures make car manufacturers very careful in this area.

It is not needed to anodise 6000 and 5000 series alloys (these being the main alloy families used in car auto bodies to stop corrosion), the natural resistance of the alloy itself is taken into account by the engineers. Shipmakers and car makers especially try to reduce costs and anodising would in fact of been a hinderence to the joining (laser welding for the A2) by arcing during the welding process of the space frame. Anodising is mainly there for decorative purposes and is only adding more oxide in anycase.

I am very sure that our A2's are in robust health generally as far as the body is concerned.
 

Alan_uk

A2OC Donor
Hi Mark

Many thanks for a comprehensive reply. I'm sleeping more soundly already, zzzzzzzzzzzz
 

Skipton01

Well-Known Member
Re the door hinges. To be honest I haven't taken much notice here as my A2 is OK. The hinges are a 3 piece design. Where and how are they failing?
The hinge itself isn't failing, it is the door panel that splits, where the top hinge plate bolts onto it.

The hinge is made from cast alloy and is very thick, about 5mm in section. I suspect that the door is a pressing and is a maximum of 1mm thick, which is why the failure occurs.

Cheers,

Mike
 

Mark Brigg

Member
Sorry to send you to sleep, Alan. Its just that a great deal of work has gone on in the aluminium industry together with car manufacturers to enable strong lightweight car bodies to be produced that don't fall apart in 5 minutes or 5 years. I was involved with some of that work. Just because some bike maker messed up why should other industries be tarred with ther same brush.

Mike the door pressing will be a little thicker than 1mm, perhaps as much as 1,5mm, but there is obviously an issue that there is not enough material in that position. Most cars today have welded tailored blanks pressed to produce whole doors, giving multi thicknesses in the single pressing putting metal where it is needed. Sadly aluminium tailored blanks were not developed sufficiently when the A2 was designed. It will be interesting to see Audi's solution.
 

erstens

Member
As Mike says.
See the images: http://forum.a2-freun.de/attachment.php?attachmentid=11865
http://forum.a2-freun.de/attachment.php?attachmentid=11864
http://forum.a2-freun.de/attachment.php?attachmentid=11864
The hinge is made from cast alloy and is very thick, about 5mm in section. I suspect that the door is a pressing and is a maximum of 1mm thick, which is why the failure occurs.
Behind the less than 1mm door there is a thicker sheet but we still don't have images or constructionpictures.

Edit: I now see the links don't work anymore, I will check that! Images now uploadet.
 
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erstens

Member
Mark is right as well. The door and the sheet matal behind it are sot welded together. There is some space betweel them, which causes the problem.

But there is corrosion of Aluminum.
Me as a chemist, I checked what the white powder is. It is Al(OH)3 (Aluminiumhydroxyde).
See your rear mirrors base:
 
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andyman

Member
Very interesting mark, excellent posting, I shall however go and check Ollies hinges tomorrow when the wife gets home!!
 

tdiman

Past Member
Mark is right as well. The door and the sheet matal behind it are sot welded together. There is some space betweel them, which causes the problem.

But there is corrosion of Aluminum.
Me as a chemist, I checked what the white powder is. It is Al(OH)3 (Aluminiumhydroxyde).
See your rear mirrors base:
At least I'd hope it's that or a visit from the boy's in blue might be in order ha ha ha
 

Alan_uk

A2OC Donor
Sorry to send you to sleep, Alan.
Hi Mark, I wasn't getting at your long post sending me to sleep. It was a good read. I was refering to the fact that your post was reassuring and aluding to the fact I could sleep more soundly and not worry my A2 would suddenly collapse in a heap of dust ;-)

Cheers.
 

mjs4x4

A2OC Donor
What will be most interesting is seeing how Audi try to wriggle out of it. 180,000 or so A2's sold less write offs potentially still leaves a few to fix.

Bearing in mind Audi lost money on every one they sold I can't imagine them being too keen to invest much in a recall.
 

Mark Brigg

Member
It may be that not every A2 is affected by the hinge problem. There could be some manufacturing deviations that mean that on some cars the sheetmetal on the door is mated up with the inner support, and some not as Skipton described with his A2. This could explain why some cars are afected and some not.

Sorry Alan. Yes the point is that thank goodness our A2 spaceframes were not produced by a Chinese bike maker and that we can in general be relaxed. Also any casual visitor to the sight would see that an A2 is a good ownership proposition and not a latterday Lancia Thema.

Erstens. You are right the powder is oxide - corrosion. Why is it not so serious? If that part had been uncoated steel it probably would have completly gone by now. At my fortmer company the R&D department carried out intensive studies on corrosion over many years. As per your pictures we carried out tests for the pitting type of corrosion normally characterised by steel. Samples were very accurately weighed, placed in a corrosive environment and periodically weighed over time and the weight loss recorded. It will be a very long time before there would be any concern for the part that you posted. Anodising would help, but that in itself is a process of oxidising aluminium. And the cost of anodising, our A2's were already too expensive new.
 
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