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Aluminum for Low Temperature

Aluminum for Low Temperature

Aluminum for Low Temperature

(OP)
I am trying to decide which Al alloy to use.

I have a cylinder approx 38mm long with very thin walls (<1mm along most of it). Aluminum with black anodize is really the only option due to weight and other factors so I need to determine if I should use 6061-T6 or 7075-T6. These are the only alloys that are allowed by the customer so I can't stray from those.

The temperature range is +71C down to -41C. At low temperature there is very little radial stress but the axial stress is fairly high (given the wall thickness) and I want to make sure that it will not break. I am worried about the brittleness of 7075-T6 when compared with 6061-T6.

Any suggestions?

Thanks,
Dan

RE: Aluminum for Low Temperature

Use fracture mechanics to decide what is the allowable flaw size and see if 7075 can be used.  Can you use a different temper for the 7075?  A T7-style overaging can increase toughness.

Regards,

Cory

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RE: Aluminum for Low Temperature

(OP)
Cory,
Thanks for that. I did that and they both look OK. I guess what I am really worried about is how the fracture toughness changes (if at all) when you get down to -41C.

I can't find any reference with anything but, I am assuming, at 20C and no mention of if that changes with temperature.

Dan

RE: Aluminum for Low Temperature

ASM Handbook Volume 19 Fatigue and Fracture has the following data:

Alloy       KIc @ 24 °C       KIc @ -196 °C
---------   -----------      ------------
6061-T651   29.1 MPa m0.5     41.6 MPa m0.5
7075-T651   22.5 MPa m0.5     27.6 MPa m0.5

Regards,

Cory

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RE: Aluminum for Low Temperature

(OP)
Cory,

Thats exactly what I needed, thanks.

Dan

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