The numbers used to describe aluminum wrought alloys conform to a code developed by the ALUMINUM ASSOCIATION. The first four figures in the grouping describe the alloys used. Other code figures or letters indicate the form of the product and the type of heat-treatment given.
Four Digit Numerical Designations
1st Digit – Indicates alloy group.
2nd Digit – Indicates modifications in impurity limits.
3rd & 4th Digits – Identify the different alloys in a group.
Alloy Groups
Alloy Number Major Alloying Elements
1 XXX – Aluminum – 99.00% minimum and greater
2 XXX – Copper
3 XXX – Manganese
4 XXX – Silicon
5 XXX – Magnesium
6 XXX – Magnesium & Silicon
7 XXX – Zinc
8 XXX – Other elements
9 XXX – Unused series
The letter “X” preceding a 4 digit series indicates experimental – Example – X7004.
Tempers
These designations follow the above alloy numbers.
F – as fabricated – Products which have no special control over final temper.
O – Annealed
H– Strain-hardened – where increased strength is obtained by cold work.
T – Thermally treated to produce stable tempers other than “F”, “O” or “H”.
W – Solution heat treated resulting in an unstable temper.
Subdivision of H. Temper
The first digit following an H indicates the specific combination of basic operations:
H1 – Strain-hardened only.
H2 – Strain-hardened and partially annealed.
H3 – Strain-hardened and stabilized.
H4 – Strain-hardened and lacquered or painted.
The second digit following an H indicates the degree of strain-hardening:
H x 1 – Eighth hard
H x 2 – Quarter hard
H x 4 – Half hard
H x 6 – Three-quarter hard
H x 8 – Hard
H x 9 – Extra hard
A third digit is sometimes used when the degree of control of temper or mechanical properties are different from but close to those for the two-digit H temper designation.
H111 – Applies to products, which are strain hardened less than the amount required for a controlled H11 temper.
H112 – Applies to products, which acquire some temper from shaping processes not having special control over the amount of strain hardening or thermal treatment, but for which there are mechanical property limits.
H311 – Applies to products, which are strain-hardened less than the amount required for a controlled H31 temper.
H321 – Applies to products, which are strain-hardened less than the amount required for a controlled H32 temper.
H323-H343 – Applies to products, which are specially fabricated to have acceptable resistance to stress corrosion cracking.
Subdivisions of T Temper
T1 – Cooled from an elevated temperature shaping process and naturally aged to a substantially stable condition.
T2 – Annealed (cast products only).
T3– Solution heat-treated and then cold worked.
T4 – Solution heat-treated and naturally aged to a substantially stable condition.
T5 – Cooled from an elevated temperature shaping process and then artificially aged.
T6 – Solution heat-treated and then artificially aged.
T7 – Solution heat-treated and then over aged/stabilized.
T8 – Solution heat-treated, cold worked, and then artificially aged.
T9 – Solution heat-treated, artificially aged, and then cold worked.
T10– Cooled from an elevated temperature shaping process, cold worked and then artificially aged. Additional digits may be added to indicate a variation in treatment, which significantly alters the characteristics of the product.
T x 51 – Stress-relieved by stretching.
T x 510 – Products that receive no further straightening after stretching.
T x 511– Products that may receive minor straightening after stretching to comply with standard tolerances.
T x 52 – Stress-relieved by compressing