Aluminium

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Crawfster

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As discussed in a thread elsewhere, don't let anyone convince you that your car won't rust/corrode just because it's made of aluminium.

You should see my aluminium diving cylinders - 3 years and they're distinctly "rubber ducked".

Admittedly, I have no plans to take my shiny red A2 to 35 metres of depth in warm salty water, but believe me, aluminium won't last for ever.

A titanium A2 would be the answer.....
 
LOL yeah but it would cost double possibly triple the A2's price, but god it would be fast.

1.4SE petrol 2001, Dark interior, Sat cloth, Brilliant Silver, 3 spoke Steering wheel, Rear electric windows and Panasonic MR555 stereo, Panasonic 8CD changer, 10 speakers (2 extra 13" 190 watt each.)

1.4TDiSE 2002, Biege interior, Brilliant Black, Concert II.
 
Actually isn't the point about aluminium that the surface oxides immediately thereby protecting the unoxidised layers below. So whereas a steel car will rust all the way through, an aluminium one is likely to suffer surface rust only.

I also noticed that someone on a recent thread said that aluminium would crumple like foil in a crash. Surely, this can't be correct. I thought aluminium was tough - although if anyone has any knowledge/experience of safety issues with regard to aluminium cars (especially the A2 and A8), I would be very interested to know. Are they safe?
 
Harps is right on the corrosion, surface only. This happens quite quickly, but doesn't penetrate. Well that's what my school teacher told me 14 years ago.

Audi A2 1.4SE
Build Wk40/2002 | OpenSky | Azure Blue | Climate | DIS | APS | Lumbar
 
I don't think Aluminium crumples like foil but it is definetely softer than steel. However you want cars to crumple to a certain extent to absorb the impact of a crash and slow the very soft human occupant more gradually. I'm no expert on Titanium but if anyone was mad enough to make a car out of it you could have the problem of it being too strong and not crumpling enough.

A titanium car would be cool though.
 
The "surface only" corrosion is certainly the idea with aluminium, and, under only mild circumstances, this is largely true.

However, there's no doubting that more extreme conditions, corrosion will "burrow" into the metal - well, that's what's happened to my cylinders.

Gram for gram, my understanding is that aluminium is much weaker than steel and more aluminium has to be used - which is why, for example, my steel diving cylinder is lighter than my aluminiums, and why racing bikes made of Al have thicker sections.
 
My engineering training (dim and distant past) told me that weight for weight aluminium is stronger - you use less weight to achive the same strength however you will have more volume of metal.

Having been involved in building both steel and aluminium railway vehicles it is not just the material that changes but the methods of construction with aluminium tending to be a mix of extrusions, stretch formings and panels where a steel car tends to be just pressings spot welded together.

You achieve the correct crumple performance by designing in just the right amount of strength so the shell will crumple or stay rigid as required. The principles here are no different whichever metal is used - the same principles would apply with titanium.

Apologies if it is too techie!

Ian

2002 1.4 Petrol SE, silver with climate control.
 
If you have to decide in which car you have to have an big crash, choose an A2. As the engineer who are doing crash test. This is the real advantage of aluminium. Corrosion is no topic on todays cars.

Regards,
John Dusdale
 
My old Land Rover was a mixture of steel and aluminium parts and at all places where both materials were screwed together without insulation the alu disintegrated quickly. Every contact with other metals - together with (salty) water - will destroy the alu parts of the A2 (electrolytical contact corrosion). In an Audi training booklet about alu is written that they use special rubber parts, special glue and special screws for production and repair.

A2 3L 1.2l, azur-blue with blue interior (like my old Smart…), climate control, style- + advance-package, winter package, radio "concert"
 
Yes - but have you ever seen an aluminium car burn? I've seen two Land Rovers go up in smoke - and all that was left was the engine and subframe - the shell was a puddle of molten goo! Hopefully no one reading this has had a similar experience with an A2?!

Take care out there!

Kit

Soon to be the owner of a Dolphin Grey 1.6 FSI SE with Red Leather, ECC, DIS & Symphony 6 CD
 
Corrosion is still a big topic on cars today. As Skasie indicated, the problem is basically contact corrosion. And you dont need two different materials - you can generate this effect with two pieces of aluminium. It basically comes down to the contact materials potential difference (i.e. voltage) and loads of complicated chemical stuff, that I choose to forget. The key to producing a car in aluminium is just to take care to isolate the aluminium from any chance of this type of corrosion - however in the real world this is quite tough.
This is where I get a bit fuzzy, however I think the main issuess are with things like pit corrosion, which occurs when dirt (salt etc) becomes attached to the aluminium and causes localised potential difference. This builds up and can create holes in the alu. Bit simplified, but this is the general gist.
Personally, I dont believe that aluminium has a great advantage in the corrosion stakes compared to steel, when considering all the other benefits. Both materials meet the VM's specifications, of which would have got more severe over time, however alu has the clear weight advantages.

Surely we must have a materials expert on the forum to clarify this ?

Kaine




A2 1.4Tdi SE | black | red leather | Concert | Open Sky | A2OC Stickers x2
 
Kit lewis, do you want to rebuilt the car after it was burned out? Is this a disadvantage of alu?

Regards
John Dusdale
 
The problem is Galvanic corrosion and occurs where any two metals are in contact and a current can flow. Unfortunately in our climate the rain is slightly acidic so it conducts electricity as does salt spray from the road (i.e. both are electrolytes). The problem is not limited to A2 and A8 as any car with aluminium in it (aluminium heads are common) may have the problem, at least with an aluminium car there is less steel so less of a problem. For more info see:

http://www.corrosion-doctors.org/Aircraft/galv-design.htm

Ian

2002 1.4 Petrol SE, silver with climate control.
 
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