Bonjour.
Informations trouvées sur le site de Aircraft Spruce Europe:
The letter “T” is always followed by one or more digits. These digits indicate the method used to produce the stable tempers, as follows:
-T3 Solution heat treated, then cold worked.
-T351 Solution heat treated, stress-relieved stretched, then cold worked.
-T36 Solution heat treated, then cold worked (controlled).
-T4 Solution heat treated, then naturally aged.
-T451 Solution heat treated, then stress relieved stretched.
-T5 Artificially aged only.
-T6 Solution heat treated, then artificially aged.
-T61 Solution heat treated (boiling water quench), then artificially aged.
-T651 Solution heat treated, stress-relieved stretched, then artificially aged (precipitation heat treatment).
-T652 Solution heat treated, stress relieved by compression. then artificially aged.
-T7 Solution heat treated, then stabilized.
-T8 Solution heat treated, cold worked, then artificially aged.
-T81 Solution heat treated, cold worked (controlled), then artificially aged.
-T851 Solution heat treated, cold worked, stress-relieved stretched, then artificially aged.
-T9 Solution heat treated, artificially aged, then cold worked.
-T10 Artificially aged, then cold worked.
Added digits indicate modification of standard practice.