Looking for the AMS equivalent of ASTM B221 (6061-T6)

/NOTE/ Before I give You the technical answer... here is a practical observation.
Have your vendor check the material certification-paperwork and the mil-printed-markings on the raw material. Often a OEM will manufacture a product to a high standard specification then cross-qualify all other equivalent/inferior specifications... so that superior raw product can be sold to virtually any user to any spec [listed], legitimately. IF any spec for the raw material is represented in the MMPDS is co-listed then everything is technically 'OK'.

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Your question... IF MMPDS co-lists ASTM B221 for 6061 [temper/form specific]... then 'Yes', absolutely. I quickly scanned... MIL-HDBK-5J and MMPDS-17 for 6061 in various forms/tempers... 'NO'

In ONE corporate document... ASTM B221 is listed... BUT ONLY FOR IMPACT EXTRUSIONS... a very specialized case covered by NO aerospace spec.

Refer to to MMPDS Appendix C for Specification indexes... including 'technically equivalent specs'... ASTM B221 is not listed... except for a few 'odd' alloys.

Awkwardly... there may be many reasons why this is 'so'.

In many cases a material made to an AMS spec will fully comply with the ASTM requirements, but almost never the other way.
Minor details like differences in trace chemistry, much tighter HT restrictions, and in many cases more extensive testing are what set AMS specs apart.
Complying with MMPDS requires a lot of details.

Thank you both for the input. This is helpful. The issue we have is that a supplier is making a part from 6061-T6 per ASTM B221 but we can't use that ASTM specification to justify the use of the material because B221 does not specifically appear in MMPDS for that 6061-T6. (We are being held to MMPDS). MMPDS only shows AMS 4150. But, as far as I can tell, that spec is virtually identical to the relevant section inside ASTM B221. Beyond doing a side-by-side comparison, is there any official document showing that they are, in fact, equivalent?

cripe tell the suppler that B221 material is not acceptable and to use AMS 4150. hopefully your drawing called out AMS 4150.

The only people that do this are the QA department at your supplier.
Because they are ones that would have to re-issue certificates for the material.
I have done things like this for people in the past.
For a simple fee we would review specifications and actual testing and test results.
Sometimes this was easy and other times it couldn't be done without having all of the material back for re-testing.

Seriously... there are NO other specs listed in the Mill-markings for the raw-stock in-use??? Too bad...

I'm reading ASTM B221 right now, and it's not equivalent to AMS 4150. But it might not be inferior, either.
ASTM B221 is titled "Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes", which is pretty broad, and lists dozens of candidate materials suitable for extrusion according to this process. It would take some effort to determine how close B221's definition of 6061-T6 comes to the one in AMS 4150 (and I don't have a copy of 4150).

That said, this is interesting:

That's a familiar definition to many of us... I wasn't expecting it to resemble "A-basis" so much.