A356.2 vs 6061

stickman

How do they compare?

mz__jo

Are we talking cranks here? I had a quick google for a356.2 and the chinese make it in large quantities for moulding and forging. 6061 is also made in large quantities by divers manufacturers, it's another standard material like 7005 or cro-mo, quality and qualities probably depend a lot on whose making the raw material and on how it is used and treated. The rest I will leave to the metallurgists.

Cheers Jo

stickman

Yes, cranks, They are nearly always 6061 but Sturmey Archer use mostly A356.2

mz__jo

Sunrace use A356.2 for a very budget looking mtb chainset (looks the same as the Suntour on my mtb, which really is very cheap quality) Stronglight use a variety of alloys, currently 7005 for the top of the range and 6061 for most of the rest. I am sure that the Stronglight 80 was cold-forged in something unusual but I can't remember what. Spa use something odd for their chainsets, 2014, for which they make great claims. TA use 7075 for their rings but this needs heat treating (probably after machining).
On the evidence A356.2 is probably considered inferior to 6061. Sunrace own Sturmey which might explain their use of it, or it could just be an in-house special alloy.
Cheers Jo

stickman

Thanks. It's a shame if Sturmey use lower quality than normal, but I suppose they care more about gear hubs.

mz__jo

Some metallurgist will probably come up with an arguement that the Sunrace/Sturmey offering is superior to that of TA or Stronglight but at the moment I can't really see how. My SR cranks are really rubbish but they seem to perform correctly, the shoddy part is the steel rings.
Cheers Jo

Monty Dog

6061 is heat-treatable, so if treated properly will be stronger.

mz__jo

Monty Dog wrote:

6061 is heat-treatable, so if treated properly will be stronger.

I agree; the emphasis however is on the if. If not treated correctly I doubt that there will be a significant advantage, probably the inverse. However I would trust Stronglight to do the job correctly. I would have my doubts about an unknown quantity of chinese subcontractors, for whom forging A365 is probably a more reliable process (they do have vast stocks of the stuff to sell on the web if you look, so they probably know its qualities).
With the number of chinese 7005 frames around (it is a base material for them now just like cro-mo was) I do wonder about the heat treating. Columbus make it sound a very precise process but are the chinese as careful?