Use of alum alloy at high temp, high vacuum

[petermaris]

Hi all,
I am looking for more info on the use of alum. alloy at higher temperatures (300 degr.C) and under high vacuum conditions (10-5 Torr). Is material diffusion (Zn) an issue when using the material for 2 weeks under this condition ? Any other pro/cons known ?

 

[IRstuff]

Aluminum can be annealed at temperatures as low as 100ºC, and its polycrystalline structure allows for migration along grain boundaries.

TTFN

FAQ731-376

 

[CoryPad]

Zn diffusion would not be a problem is pure aluminium were used. What is the stress? If it is low, then maybe the pure Al could be used.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[petermaris]

The stress level in the material will be low, as it is not used for structural application. Pure Al is an option, but the material is less stiff, so we will have to use additional stiffeners.(It concerns a plate of 2x2 m, which is suspended horizontal to the 'ceiling'.)
My main concern is the diffusion of Zn, which will occur for sure, but will it be relevant in 2 weeks of testing at 300 degr. C ??

 

[NickE]

Uh, I'm pretty sure (though often wrong when I am -- and someone here will tell me if I am) that the modulus of pure Al is not very different from that of common Al-Zn alloys.

Bulk content of alloys controls the modulus, the 7xxx series of Al alloys (the ones with Zn in them) have aproximately 88%wt Al, thus governing the slope of the elastic portion of the stress/strain curve.

Looking in my GEM - AM&P Dec. 2001 -- I see that 2024/6061 are right around 73GPa and 7079 is given as 71GPa. so around 3% difference.

How about using an alloy that contains no Zn?

Nick
I love materials science!