How to get 356-T6 aluminum back to weak state?

[BrianE22]

Some of the castings we get from the foundry aren't quite as straight as I'd like. I'd like to pull those out, weaken them, hammer them straighter and then re-heat to T6 state. What do I need to do to get the part back to the weak (as cast) state?

 

[metengr]

You would anneal the castings and re-heat treat them back to the T6 condition. Annealing is done
around 300-400˚C (575-750˚F).

 

[Lyrl]

Not sure if you plan on outsourcing the rehardening after the parts are straight. If you plan to do it in house, note that going back to the T6 state requires a solutioning furnace with a water quench tank.

 

[WKTaylor]

BrianE22... as I suspected...

Suggest review of AMS2771 Rev E Heat Treatment of Aluminum Alloy Castings

Rationale [for Rev E]...
AMS2771E results from a limited scope ballot to clarify when refrigeration may be used for retention of the AQ condition or to facilitate straightening (3.2.10).

Take the -T6 Casting: solution HT and quench it; immediately freeze [0F] after quenching; remove castings from cold storage [one-at-a-time] for straightening while in AQ [W] Temper; then age HT straightened castings [back] to -T6 temper.

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]

 

[BrianE22]

Thanks everyone -

 

[tbuelna]

BrianE22-

If you foresee this being an ongoing issue, I would recommend looking into what is actually causing the distortion. Mechanical straightening addresses a symptom rather than the root cause. If the distortion is created during the heat treatment process, then look at modifying your heat treat process. If the distortion is created during solidification of the casting, then look at modifying your tooling and/or design of the casting itself. Changes to your heat treat process should not cost much. Changes to your tooling or casting design will involve some cost depending how extensive they are. If the casting is being produced in any significant quantity, then the cost for these changes would likely be offset by eliminating the manual straightening procedure.

Here is a helpful article from the AFS:

http://www.afsinc.org/about/content.cfm?ItemNumber=10466

 

[BrianE22]

That's a good point on the possible distortion after initial straightening and then after the subsequent heat treating. I'll try to get a handle on that.

 

[FennLane]

Its never a great idea to introduce a residual stress and then heat treat and expect the part not to move.

The most significant residual stress will probably due to the quenching process involved in solution treatment and if this is the cause of distortion you may struggle.

What are they like as raw castings before solution treatment?

It may be worth looking at quenching into water at between 70 and 80 degC to reduce distortion.

 

[WKTaylor]

BrianE22..

That's a good point on the possible distortion after initial straightening and then after the subsequent heat treating. I'll try to get a handle on that.


As I mentioned in my original post, best time to straighten [or stretch/cold-work] aluminum alloys [including castings] is in the post-quench unstable 'W' temper. In this case the major distortion potential at the time of quench is BEFORE the straightening! After straightening in W temper [work fast], then a low temperature bake is required to [re] attain -T6 temper Potential for warpage in the low-temp [long-bake] is minimal.**

**NOTE: this is not the only path to -T6, but is fastest. However, it might make sense to allow natural aging to -T4 to RT stabilize the casting 'as straightened'... then bake-age to -T6.

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]