The numbers used to describe wrought aluminum alloys follow a code developed by the Aluminum Association. The first four digits describe the alloy; additional letters and digits indicate the product form and the type of heat treatment.
Four-digit numerical designations
- 1st digit Alloy group
- 2nd digit Modifications in impurity limits
- 3rd & 4th Identify the alloy within the group
Alloy groups
| Series | Major alloying element |
|---|---|
| 1xxx | Aluminum — 99.00% minimum and greater |
| 2xxx | Copper |
| 3xxx | Manganese |
| 4xxx | Silicon |
| 5xxx | Magnesium |
| 6xxx | Magnesium & silicon |
| 7xxx | Zinc |
| 8xxx | Other elements |
| 9xxx | Unused series |
The letter “X” in front of a four-digit number indicates an experimental alloy — for example X7004.
Tempers
Temper designations follow the alloy number.
- F As fabricated — no special control over the final temper
- O Annealed
- H Strain-hardened — strength increased by cold work
- T Thermally treated to produce stable tempers other than F, O or H
- W Solution heat-treated — an unstable temper
Subdivisions of the H temper
The first digit after the H indicates the 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 indicates the degree of strain-hardening:
- Hx1 Eighth hard
- Hx2 Quarter hard
- Hx4 Half hard
- Hx6 Three-quarter hard
- Hx8 Hard
- Hx9 Extra hard
A third digit is sometimes used when the degree of control of temper or the mechanical properties differ from, but are close to, those of the two-digit H temper:
- H111 — products strain-hardened less than the amount required for a controlled H11 temper.
- H112 — products that acquire some temper from shaping processes without special control over strain-hardening or thermal treatment, but for which there are mechanical property limits.
- H311 — products strain-hardened less than the amount required for a controlled H31 temper.
- H321 — products strain-hardened less than the amount required for a controlled H32 temper.
- H323–H343 — products specially fabricated to have acceptable resistance to stress-corrosion cracking.
Subdivisions of the T temper
| Temper | Meaning |
|---|---|
| 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, then cold worked |
| T4 | Solution heat-treated and naturally aged to a substantially stable condition |
| T5 | Cooled from an elevated-temperature shaping process, then artificially aged |
| T6 | Solution heat-treated, then artificially aged |
| T7 | Solution heat-treated, then overaged / stabilized |
| T8 | Solution heat-treated, cold worked, then artificially aged |
| T9 | Solution heat-treated, artificially aged, then cold worked |
| T10 | Cooled from an elevated-temperature shaping process, cold worked, then artificially aged |
Additional digits may be added to indicate a variation in treatment that significantly alters the characteristics of the product:
- Tx51 Stress-relieved by stretching
- Tx510 No further straightening after stretching
- Tx511 Minor straightening after stretching to meet standard tolerances
- Tx52 Stress-relieved by compressing