Vacuum grade aluminium thicknesses, forging and porosity....

[simonwar]

Can anyone clarify?

I am told that billet aluminium is supplied forged to a degree, and that each time the billet is forged, the aluminium loses its porosity.

I want to investigate fabricating a high vacumm vessel, (10E-9T) using aluminium and not sure whether to machine from solid or fabricate with individual panels. Because the chamber is 750 x750 x 2200mm my concern that the billet to manufacture this will not have been forged and have relatively higher porosity and potentially poor vacuum performance properties.

We use EN AW-6016 T6 for standard chambers at the moment.

Any help appreciated, Simon.

 

[CoryPad]

Any wrought Al alloy (sheet, plate, extrusion, forging) will be "pore-free" so that it could be used for vacuum applications. The reason to use a one-piece forging is to avoid joints, which would be the major leak sources.

Regards,

Cory

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

 

[simonwar]

Cory,

You said

"Any wrought Al alloy (sheet, plate, extrusion, forging) will be "pore-free" so that it could be used for vacuum applications".

What do you mean exactly ?

Are you saying that Al Alloy's are "pore-free", or are you saying they should be "pore-free".

To clarify my question as I know its a bit vague.

Q. Is their a guarantee of non-porosity in billet aluminium that has not had any work,like forging, done to it?

Cheers, Simon.

 

[CoryPad]

How is/was your billet produced? Was it cast? Extruded? Forged? If it is cast, then it will have porosity (~ 3%). If it was extruded or forged, it will have essentially zero porosity.



Regards,

Cory

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

 

[simonwar]

Cory,

I am in discussion with the supplier. They have to talk to Russia, where the billet comes from.

However, we believe the billet is forged to size, and I am only assuming, this is done by taking smaller thickness plate/sheet and forging up. However I am awaiting answers to these questions.

Any more questions you can think of great.

Regards, Simon.