Alloy frames going "dead"...

[Wold Ranger]

Re: Aluminium

Aluminium does age and soften over time, eventually it will literally fall apart and become soft and crumbly.

Can you give a sense of how long this takes? I've got cranks that are 20, 30, even 40 years old, and I haven't noticed them getting soft. Should I expect them to begin to get floppier gradually, or will I go to my bike one day and find a heap of dust where my cranks once were? What about my 1960s Campag hubs, or my 1950s GB brakes? What about the statue of Eros in Piccadilly Circus?

I know aluminium can corrode in certain conditions, but I don't think that's what we're discussing.

Generally a long time, depending upon conditions, but heat and cold accelerate this rate. Cranks are more likely to crack around the tapers as they become older, which is commonly recognised, but dependant on how many watts you put through them (or drop offs you do, in my case) remember we are talking mtb here, so stresses are very different, but not necessarily any less.
An Aluminium frame may feel dead after 5 years or more hard use, but probably won't break, but nothing kills a frame faster than riding in very cold conditions, like we have at present, as Aluminium becomes brittle and prone to fracture.

7000 series is harder, denser and heavier but less prone to this ageing process, 6000 is lighter and softer and does age much faster. This is fact and not a myth, the ageing process will almost certainly affect the ride quality, but will vary from Aluminium to Aluminium.

Are you equating hardness with stiffness?

 

[one-eyed_jim]

Re: Aluminium

Cranks are more likely to crack around the tapers as they become older, which is commonly recognised, but dependant on how many watts you put through them (or drop offs you do, in my case) remember we are talking mtb here, so stresses are very different, but not necessarily any less.

But cracks in cranks, like cracks in frames, are due to accumulated fatigue in highly stressed parts of the metal, not to do with the metal becoming soft or crumbly with age and use. Until the cracks become visible (or audible) there isn't any change in the stiffness of the crank. At a distance from the failure, the metal is as hard and as stiff as when it was made. I rode a pair of XT 730 cranks for a long time with a crack slowly growing between the right arm and the spider. I kept an eye on it, and retired the crank before it grew too far, but if I hadn't spotted it while I was cleaning the bike, nothing about the behaviour of the crank would have told me it was there.

An Aluminium frame may feel dead after 5 years or more hard use

It may - but then again it may not. I don't know of any rational reason why it would, but people can be really good at feeling things that aren't there.

 

[perry]

this is interesting

http://www.motorcycledaily.com/21may03s ... sframe.htm

makes me wonder how good a well made steel full sus would be with current linkage designs

this bit makes me wonder if the idea of aluminum dieing is just the owner getting used to its Idiosyncrasy over time

"A good example is Honda's RC45 superbike, which was considered a beast in its first year on the track, but was acclaimed as "great" (by at least one factory superbike star) in the last season before it was replaced by the RC51"

 

[Wold Ranger]

Steel

Still think steel would be on the heavy side for a full suss frame? Soft tails excepted of course!

 

[Neil G]

necrofiliacs , aluminum frames were dead to begin with

http://www.bmxbasics.org/new/bmx0398.html

http://www.bmxbasics.org/new/bmx0702.html

That's a crazy pic of that frame letting go on that double!

TBH I've seen some really dramatic failures on BMX frames from cracked headtubes to flared/crumpled downtubes (4130 cro-mo) but in many cases if the frames had been aluminum they would have failed completely rather than deforming.

Don't really buy the concept of alminium frames gong 'dead' but do believe that they become weaker with constant use/abuse just due to the flexing and fatigue that a frame has to go through

 

[Monty Zoomer]

Why are things never as simple as they seem

Regarding the definition of an alloy,
from my study days I recall that an 'alloy' was defined as being a particular mixture of components that has a specific chemical composition. The term was originally only used to describe mixtures containing a metal, but in general use the term is used to describe all mixtures of components.

So you could say that even Iron( the material not the element) is also an alloy as Iron can contain less than 0.05wt% Carbon and other elements such as Si, from 0.05 to 0.2wt% Carbon you have mild or low - carbon steel.

As for the properties of precipitation hardened aluminium alloys there is more than one phenomenon to consider and it’s much too late now to go into that, I will add some comments in the am.

 

[Monty Zoomer]

Here's a wierd one.

Back in the day I remember reading in MTB mags about how alloy frames were reknown for going "dead" as they aged. I.e they lost all zest and ended up feeling dull to ride.

MBUK (and the like) implied this was down to extensive use and over time this would happen to all alloy frames.



We dont hear much talk of this these days. Is that because its a myth?

I like this question, never seen a valid explanation of why this would happen or what mechanism is involved sure would like to know though, I also read in bike mags from the past that aluminium frames would became ‘baggy’ with use, whatever that means.


Aluminium fames are often referred to as feeling more dead than steel frames anyway and this is often explained as being due to the extra stiffness of the aluminium frame, this would make sense as an overly stiff frame would have much less flex and this can be explained by the need for aluminium frames to be ‘over engineered’ in order to delay the onset of fatigue cracks from cyclic stress.

Suppose first we need to clarify if we are saying that the frames are becoming more stiff as they age and therefore increasing the ‘dead’ feeling or are they becoming less stiff due to the material over ageing and loosing strength, but if this was the case would this not produce a more flexible frame rather than a one that feels ‘dead’. It’s true that age hardened aluminium will begin to soften after it’s reached its peak strength but this is a very slow process unless you keep your bike in the oven.