Retrogressed and Re-Aged 7076-T6

[WKTaylor]

Folks...

"Anyone-out-there" [DoD org, company, etc] using any form of the retrogression and re-aging heat treat processes [RRA-HT] for newly fabricated, or existing [old], 7075-T6 [-T6-RRA] parts FOR REAL???

I understand some huge benefits due to greatly increased SCC & exfoliation corrosion thresholds... almost to the capability of -T73 [-T76??] but with just a couple of KSI loss in FTu, FTy & FCy... and very little change in other properties from 7075-T6 "A" basis allowables [ref MIL-5 & MMPDS]. I also see the RRA-HT has been tested with other 7XXX alloys.

I Understand that ALCOA is using RRA-HT on their new 7XXX alloys... and giving them the -T77xxx proprietary HT designations [which also includes some intermediate stage cold-working].

Sooooo... the process appears to work... but does it have merit and any advocates for repair or replacement of existing parts [Depot or Major repair]???.

The obvious value for the RRA HT is ability to maintain the relative strength of 7075-T6 parts without seriously fretting over SCC & EXCO... problems plaguing the alloy in thick sections... even when shot-peened and buried in coatings, sealant and use of low-interference-fit fasteners.

Just so I am clear... The RRA process and some test applications are described in the following articles and documents.

http://www.udri.udayton.edu/NR/exeres/360D542B-1F6A-4FF3-B51C-FDEF8137A316.htm

http://www.tms.org/pubs/journals/JOM/JOMbyIssue.asp?issue=JOM\2003\January

[lower section of the page]

http://desp.udri.udayton.edu/task_order_RZ01_Sjoblom.htm

http://stinet.dtic.mil/cgi-bin/GetTRDoc?AD=A392453&Location=U2&doc=GetTRDoc.pdf

http://findarticles.com/p/articles/mi_qa5348/is_200301/ai_n21325163

Regards, Wil Taylor

 

[Rob130]

Will, I am fairly certain the C-130 engine truss mounts have been modified to 7075-T73. This was due to both corrosion and cracking problems in the mid-late 80's. I can provide a contact name at the US Coast Guard repair center who could offer additional information. Send me a pm and I will make the introductions.

Rob

 

[WKTaylor]

Rob130..

I've seen the cracking problems with 7075-T6 die forged C-130 truss-mounts first hand... especially when abusively anodized WO shot-peening [anodize-crazing accelerates cracking tendency]

I am really looking for any application of RAA process to the -T6 temper... in-lieu-of over-aging to the -T73 temper.

Any info on 7075-T6-RAA applications???

Regards, Wil Taylor