WKTaylor
Active member
- Sep 24, 2001
- 4,062
Folks... HELP!!! [I posted this in aircraft engineeering forum... but not responses, yet]
"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 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.
[lower section of the page]
Regards, Wil Taylor
"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 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.
[lower section of the page]
Regards, Wil Taylor
