ANNEALING 7076-T6511 EXTRUSION 2

[R. Reifenberger]

Request viability/implications of annealing a 7075-T6511 extrusion to W condition to support forming process, forming the extrusion, and then heat treating per AMS 2770 to T6 condition.

 

[berkshire]

You are dealing with an extrusion that has been heat treated , mechanically cold worked and aged. Heat treating to the W temper is not Annealing, Annealing will take the material back to the O temper.
Heat treating to the W temper is commonly done for forming processes, this is an unstable temper, the material will then regain its strength slowly , but unless you mechanically cold work the material as part of the forming process , you will only get back to the T6 temper . Is this going to be strong enough for your application?
B.E.


You are judged not by what you know, but by what you can do.

 

[R. Reifenberger]

T6 will provide a sufficient MS for the application. Thank you.

 

[WKTaylor]

RR...

1. You will obviously wipe out the heat treat [HT, -T6___] and strain-relief/straightening [SRS, -T_511] when You begin this process... but You should arrive at the destination You intended.

NOTE. IF this is a standard practice, then start with extruded 7075-O material... You will 'get-there' without having to procure the 'premium' HT+SRS material.

NOTE. IF this is for a joggled/minor-formed part, then hot-joggle/form without HT [and everything else it entails]. During this process, the part is rapidly heated locally then locally formed when very hot [lowers the plastic yield]... then cooled-down rapidly. Without any further action, the part can simply be trimmed and finished. The very quick heat exposure has created 'no-harm, no-foul' to the finished part [within specific limits].

NOTE. Hot-joggling/forming is a 'lost art'... similar to 'Hot-Dimpling'.

2. "Request viability/implications of annealing a 7075-T6511 extrusion to W condition to support forming process, forming the extrusion, and then heat treating per AMS 2770 to T6 condition."

Here is how I would write this for an engineering disposition.

Solution HT/quench the 7076-T6511 extrusion to attain 'W' temper per AMS2770 or AMS-H-6088.

NOTE.
Immediately after quenching, it is optional to place the raw stock in a deep freeze [-30F] state to preserve the transition temper for X-hours prior to future forming operation.

Form/straighten the part while in the W15 to W30 temper [15--30 minutes after quench, or after removal from deep freeze].

Age harden HT part to -T62 temper per AMS2770 or AMS-H-6088. Ensure part is adequately supported to prevent distortion during the AHT bake operation.

Accomplish hardness and conductivity inspection after AHT process to verify response to HT, multiple locations
AMS2770... see AMS2658
AMS-H-6088... refer to embedded Table IX

Apply corrosion protective finishes per drawing.




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]

 

[R. Reifenberger]

The information is appreciated. The organization I support often has difficulty obtaining some materials and they look for ways to work with what they have to meet production schedules. The parts that are locally manufactured are essentially "one-offs" required when the parts cannot be obtained from the OEM.

My concern is the effect of multiple heat treatments - specifically the limitation in AMS 2770 (para. 3.3.5) to one additional solution heat treatment of material between .020-.125 inch (I'm dealing with .062 inch material). That limitation is specific to Alclad parts, which does not pertain to my specific case. However I can't seem to find much in the literature concerning the effect of multiple heat treat processes beyond that reference.

 

[WKTaylor]

RR... very familiar with all You are discussing...

AMS2770 Para 3.3.5 does NOT apply to non-clad materials. This warning is due to cladding dissolution into the surface of the base alloy... essentially crippling/ruining the alloy.... in thin sheet the degradation is immediate. A quick check of MMPDS reveals the dramatic strength differences between thin clad sheet and the [same-everything-else] bare sheet, to begin with... and clad sheet mechanical/fracture properties really 'toilet-tank' with cladding migration.

Typically, very thin clad sheet is allowed 1-solution HT... hence very thin parts that have to be formed in the -O or -W temper are always made from -O clad sheet. The one-time HT operation allowed is sufficient for parts fabrication to 2024-T42/-T62 or 7075-T62... again... ONE TIME.

IF very thin clad sheet material is procured in any other temper [-T3xx, T81xx or -T6xx] it MUST be used in that temper 'as-is'. The only exception to this rule is that 2024-T3 or -T42 sheet may be formed, within strain limit constraints, then may be aged HT to -T81 or -T62 [respectively, which is also a genuine stress relief operation, well-below cladding dissolution temp].

For wrought bare aluminum alloys the general rule is minimize repetitive SHT/quench simply because warpage and distortion and [possibly] superficial corrosion and potential for shop screw-ups [somewhere in the HT process] will take it's toll... and result in useless parts [I have seen this happen]. NOT to mention the shear waste of time/resources repeating a very precise process on a relatively cheap part [usually].

One last comment. When the OEM temper has been wiped-out, by 'user heat treatment', there is no going back-to-it.

NOTE.
The temper code -T6511 tells met that the material is carefully stretch-strain-relieved/straightened by the OEM when in the '-W' temper... and that -T6 is the HT temper. Typically, even though -T6 and -T6511 have virtually identical mechanical properties [MMPDS], the stretch-strain-relief operation tends to improve corrosion and stress-corrosion cracking resistance and to make the material 'more stable' [less distortion-prone] when trimmed/cut/machined/peened/etc.

RR... NOTE.
You don't seem to be on the military global listing.



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]