MRS Specification on 2024-T3 Sheet Stock 4

[YoungTurk]

Please see:

http://www.eng-tips.com/viewthread.cfm?qid=319891

Hoping someone here has some input.

I'm told the MRS stands for "minimum residual stress" and I see it is made by Alcoa. It has been mentioned on this site a few times, but no mention of whether the standard material properties are still applicable.

 

[YoungTurk]

To be clear, a supplier is offering 2024-T3 sheet stock specified as "2024-T3 MRS" on the material cert. Supplier states this is "minimum residual stress" type material.

This specification was mentioned on this site here:

http://www.eng-tips.com/viewthread.cfm?qid=103157

Looking for more info, especially MRS specification or statement that existing specifications apply.

 

[WKTaylor]

MRS sheet aluminum...

MRS plate aluminum is pretty common stuff: -T351, -T651, -T7351,-T851 etc. Plate aluminum can be stress relieved in the "W" temper by lightly stretching it a few percent [1--3%]. Plate aluminum [0.250 and thicker] can be reliably stretched without the spontaneous appearance of odd surface deformations such as wavieness and luder's lines.

MRS sheet [less than 0.249 thick] is pretty unusual stuff. It must be stretched very carefully and to avoid these surface imperfections that can ruin the sheet. For this reason sheet is rarely stretched for stress relief and the tempers reflect this contition: -T3, -T6, -T73, -T81, etc. MRS Sheet is typically used only in the flat or wrap-around state: NO forming advised. Typically MRS sheet is used for flat skins, webs, etc. IF MRS sheet is formed in the heat treated condition [stretch-formed, bent, etc], the MRS sheet has a strong tendency to form luders lines and/or standing wavieness which has a negative affect on visual quality.

NOTE: one way OEMs stress relieve stretch-formed parts is by leaving them in the stressed [stretched] state; then exposing the aluminum materials to aging temperatures for a brief period [typically 1--3 hours].

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[KirbyWan]

I've had so specify Aluminum sheet as MRS (minimum residual stress)in one instance where we were chem milling .025 thick material down to .013 thick. Without the MRS material it curled up as it was chem milled as all those residual stresses were released. The chem miller recommended we order the material as MRS, which that thin was a major pain the but, because it would have been a special order. We ended up ordering .032 thick and having the supplier machine it to thickness before sending it to the chem millers.

That said it has the same properties as the equivalent grade/temper of aluminum.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[YoungTurk]

Thanks guys.

I've suggested our purchasing not accept the MRS material in lieu of standard 2024-T3 based partially on Wil's comments about difficulties in making formed parts from it, as well as the possibility that our inspection department would request engineering coverage to update material callouts with the MRS designator to match the material certs.

Supplier did state material still met QQ-A-250/5, though I am still wondering whether the statement / assumption that the additional stress relieving has no impact on material properties is backed by any process specification or similar? I'd expect minor changes in some properties due to the stretching, though they would probably negligible for the majority of what we would use it for here.