AL 2024 T351 vs. AL 2024 T361

A. This is a heat treating question as the "T" designation following the alloy designates the tempering process that the alloy was subjected to. Only a finisher that knows heat treatment of aluminum (or has an ASM Metals Handbook) will be able to answer this one. From various internet sites, perhaps the following will indicate the difference in properties which would explain why a designer would specify -T351, for instance, over -T361.

T351 temper 2024 plate has an ultimate tensile strength of at least 57,000 - 62,000 psi (393 - 427 MPa) and yield strength of 40,000 - 41,000 psi (276-282 MPa). It has elongation of 4-12%. While T361 has slightly better ultimate tensile strength (72 ksi for T361 vs. 68 ksi for T351), T361 exhibits much higher yield strength (47 vs. 57 ksi).

A. Just wanted to follow up on the other commenter's response. Yes, it's correct that the yield and ultimate strengths of T361 are higher than T351, so if you have a high stress application you might need the extra tempering. That said, T361 is also slightly more brittle, which you can tell by the ratio of yield strength to ultimate. The closer the two values, the more brittle the material. 2024 has the best fatigue properties of all the aluminum alloys that I'm aware of, which is why it's commonly used in gears. But if you don't need 57 ksi yield and your application has lots of cycling, you might be safer picking the T351. Not sure exactly on that. You should check MIL testing for a better answer.

7075 is another alternative, which has an even higher yield strength. But it's a bit less common and more difficult to machine.