2024-T8?

[bnrg]

Hello,
I have an application that will have short term (~1hr) exposure to a hot environment which may be as high as 300-325 F. In looking at what I have used before for similar items (7075-T7351, tho only to 275 F) and possible alternates I came across 2024-T8 which (using mil-hdbk-5 data) really looks much better than 7075 in terms of strength and modulus, and any other aluminum as well. Weight is the driver, and CRES/Ti are not attractive for this. The other tempers of 2024 have SCC concerns and while this is not a major concern in this application, I prefer to avoid this if possible and the T8 looks very attractive, tho somewhat pricy and with limited availability. Those 2 aside, are there any aspects of 2024-T8 that are negatives?

Thanks

 

[racookpe1978]

300-325 F is hot, but not very close to many metal temperature limits.

1. Are you sure its 325 F, and not 325 deg C?
2. How many times will the part (or parts ?) be heated to 325, and how close are your stress/strain/stretch and yield limits at 325?

Seems like you're not likely to approach prudent design limits (reasonable safety factors) if you have strong operational and maintenance controls on the process.

 

[3DDave]

I'd contact Alcoa. Their PDF on 2024 products indicates they think the 250F is high temp use.

Sheet products, usually alclad, are used extensively in commercial and military aircraft for fuselage skins,
wing skins and engine areas where elevated temperatures to 250°F (121°C) are often encountered.

This contrast with Alcoa statements about 2124

A P P L I C A T I O N S
Alloy 2124-T851 is recommended for moderately elevated temperature applications (250-350°F,
121-177°C) requiring better short-transverse ductility and fracture toughness guarantees than are
available with 2024-T851 plate.

 

[tbuelna]

You did not mention the material form, but for plate you might take a look at 2219-T851. Comparable to 2024-T851 at the temperature range you noted, but a bit better up to 600degF. Except for plate form, 2024 might have better availability than 2219. For your reference attached are the Ftu @ time/temp curves for 2024-T851 & 2219-T851.

 

[bnrg]

Thank you for the comments-2219 really looks good as does 2124 for hot, but availability is something else. Alcoa no quoted as they have a 7000 lb min order but they did refer me to a distributer who might have something. Parts need at least 5" diameter bar or plate and that is not too available, tho I have a few quotes for 2024-T81 round bar. The 2024-T8 precip treatment is at 375 F for 8 hours so I do feel comfortable at my temp, which is up to 325 F. My elevated temp is for an hour at longish intervals, and HDBK 5 has data for exposure time. Buckling is my main concern with this part rather than stress-stresses are low.

 

[rb1957]

the "trifector" of strength properties are static strength, fatigue strength, and corrosion performance.

2024 is good in fatigue but suspect in the others
7075 is good in static but suspect in the others,
2024T8 is good for corrosion but suspect in the others;
spot the trend ?

if the temper temp is 375 and you're going to 325, there would be much strength after some duration, and fatigue may be a serious limitation.

How big is this part ? (to make weight such a driver) ?

what is the thermal cycle like ? (375 - RT once a day ? once an hour ??)

what sort of structure are we looking at ?? thin gauge s/m ? machining ??

another day in paradise, or is paradise one day closer ?