Effect of Elevated Temperature on UTS of Aluminium 2

[SlipperyPete]

I have a question regarding the degradation in mechanical properties of 6061-T6 aluminium alloy at elevated temperatures.

The application involves operation at 250degC which creates quite a severe reduction in the strength properties. If I review published data (ESDU, MMPDS-4 etc) there are heat factor curves typically for 1hr, 10hr, 1000hr and 10,000hr soak times. For my application it will only be subjected to the elevated temperature for a maximum of 10-hours in any usage cycle. However, over the life of the vehicle the total exposure time will run into thousands of hours.

My interpretation is that the 10-hour curve should be used as this is the maximum soak time. However, I have had conflicting advice that the effect is cumulative and therefore the 10,000-hour curve should be used. At the operating temperatures at which this equipment is exposed this will make a big difference in the allowable strength properties.

Any advice gratefully received!

Peter

 

[EdStainless]

You need to consider the total cumulative time for this application.
Use the 10,000 hr curve.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[metengr]

Over-aging would be cumulative damage because this is an age hardenable material.

 

[SlipperyPete]

Thanks for the replies. To err on the safe side I probably need to stick with the 10,000-hour curve

 

[WKTaylor]

SlipperyPete...

Aluminum is a VERY poor choice for material in the temperature range You've noted... especially 6061.

6061-T6 is service rated ~300F... but anything more than VERY short spikes [a few minutes] at 250C/485F will degrade it to an oxidized and annealed condition very swiftly.

The only structural material I am aware of that can sustain operational temps at 350F [barely] is 2219-T6... and that should be anodized or [better] IVD [pure] aluminum coated to minimize oxidation.

Unsure what aluminum alloys are used for high performance pistons... but they would be 'best suited' for sustained high temp/stress operations.... but 485F is a sketchy 'stretch' for any aluminum alloy.

HOWEVER IF You really see a steady 485F, and minimum mass combined with strength/stiffness retention is required, then You need to consider titanium or steel alloys... with anodic, metallic or ceramic coatings for an oxidizing atmosphere.



Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[SlipperyPete]

Many thanks for your response Wil. I intend to argue against the use of this material and will use your response as additional ammunition!