Kingnero...
There are several scientific ways to ID the aluminum alloy-temper. Here's how I would tell a junior engineer to ID an unknown aircraft grade of aluminum [most methods/techniques] are useful for non-aerospace grades of aluminum also.
1. Strip a section of the case down to bare metal.
2. Take micro-hardness and conductivity [%IACS] readings of the bare aluminum surface. Several ASTM, MIL and AMS specs available to accomplish this testing.
3. 'Hit it' with [hand-held] spectrograph, to determine alloy composition [common lab equipment, now-days].
4. Refer to specific [suspected] alloy specifications, and/or typical wrought aluminum spec like ASTM [B221], various AMS specs or perhaps Aluminum Association Standards Data [latest like 2013], for alloy chemistry.
Between hardness, conductivity [%IACS] and chemistry You should quickly zero in-on the alloy [or closely related alloys] and relative temper [heat treated and/or strain hardened] of the case material.
Another approach would be to refer the to: DOD-HDBK-249 METALS AND ALLOYS, RAPID ON-SITE IDENTIFICATION OF (RECOMMENDED PROCEDURE FOR CHEMICAL SPOT TESTING AND ASSOCIATED PHYSICAL TESTS TO VERIFY METAL ALLOY CLASSIFICATION) ... although I've found this more useful for non-ferrous alloys.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]
