stress releif of 356 Aluminum 1

[BobM3]

I'm hoping I can avoid a trip to the local university to check the ASTM materials book. Can anyone tell me the procedure for stress relieving 356-T6 (time and temp)? I'm having problems with a plate that doesn't want to stay flat when pulled out of the mill. I'm thinking it is has too much residual stress from the casting process. Would the part normally be laid flat in the oven?

 

[swall]

If you stress relieve 356-T6, you will destroy the T6 properties, as the stress relief temp is higher than the ageing temp. A little more information on your casting, heat treat and processing sequence would help us figure out what you are trying to do.

 

[BobM3]

The casting is roughly 8" x 10" and .50" thick. Bosses on both sides need to get machined so that both sides are flat and parallel. We've double disk grinded them for years and were able to get both sides parallel but not flat. Now we're trying to rough mill both sides first to get a flat surface. We might be able to live with the reduced strength.

 

[mjh368]

hey while your in your ASM book can i get some asm 2770 or mil-h-6088. still looking for temp and time to stress relieve 2024 T3

 

[MikeHalloran]

You may not yet appreciate how soft the -0 temper is. You may be able to bend that part permanently with your bare hands. Definitely by dropping it on the table.



Mike Halloran
Pembroke Pines, FL, USA

 

[swall]

You may be able to get by with a T7 heat treatment. This will reduce the residual stresses at a cost of about a 10% reduction in tensile strength compared to T6. For sand castings, T7 is 3-5 hours at 400F; for permanent mold it is 7-9 hours at 440F. This is after the solutionize/quench, of course.

 

[BobM3]

Any of you guys have experience with the cryogenic treatment of aluminum (same part, 6061 T6 sand cast) for stress relief? A local vendor told me the following:

"After the cryogenic process we do heat up the parts to 300 degrees F. to stabilize the material. Or parts are run through an artificial aging process after cryotreating. During the artificial aging process parts are heated up to 500 degrees F."

My question: Wouldn't heating it to 500 F decrease the strength significantly?

 

[swall]

Yes, 500F is well beyond the temperature for ageing aluminum . Ageing temp for 6061 is 320-350F.