1. Aluminum Alloy Designation Rules and Code Meanings
The alloy designation system is fundamentally based on the Aluminum Association (AA) standards from the United States, utilizing a four-digit number to represent various alloys.
(1)First Digit (Thousands Place)
1xxx : Pure Aluminum (Al purity ≥ 99.00%)
2xxx : Al-Cu Alloys (e.g., Duralumin, Forging Alloys)
3xxx : Al-Mn Alloys
4xxx : Al-Si Alloys (e.g., Brazing filler metals)
5xxx : Al-Mg Alloys
6xxx : Al-Mg-Si Alloys (e.g., Forging Alloys)
7xxx : Al-Zn-Mg Alloys
8xxx : Alloys other than the above series (e.g., Al-Li, Al-Fe)
9xxx : (Reserved for future series)
(2)Second Digit (Hundreds Place)
Represented by digits 0 through 9.
For alloy series (2xxx-8xxx): The digit 0 indicates the original or basic alloy composition. Digits 1 through 9 designate various modifications of the basic alloy (e.g., impurity limits or minor element adjustments) or designations for recycled alloys with specific composition controls.
For pure aluminum (1xxx series): The digit 0 indicates no special control over individual impurities (natural impurity limits apply). Digits 1 through 9 indicate special control is exercised over one or more individual impurities, with specific limits imposed.
(3)Third and Fourth Digits (Tens and Units Place)
For pure aluminum (1xxx series): These two digits indicate the purity level of the aluminum, expressed as the two digits to the right of the decimal point in the minimum aluminum percentage (e.g., 1050 means minimum 99.50% Al).
For alloy series (2xxx-8xxx): These digits serve to differentiate between specific alloy compositions within the same series. They are often derived from legacy designations used in historical US or Japanese aluminum specifications, or simply assigned sequentially to identify unique alloy compositions.
2. Aluminum Alloy Temper Designation System
Basic Temper Designations
There are 5 basic temper designations, as shown in the table below.
| Code |
Name |
Description and Application |
| F |
As Fabricated |
Applies to products shaped during manufacturing processes (e.g., rolling, extrusion) where no special control over thermal treatment or strain hardening is employed. Mechanical property limits are typically not specified for this temper. |
| O |
Annealed |
Applies to wrought products that are fully annealed to obtain the lowest strength and maximum ductility condition. |
| H |
Strain Hardened (Work Hardened) |
Applies to products whose strength is increased by strain hardening (cold working), with or without supplementary heat treatment (such as partial annealing or stabilization) which results in some reduction in strength. The H designation is always followed by two or three Arabic numerals indicating specific processing. |
| W |
Solution Heat Treated |
An unstable temper applicable only to alloys that age naturally at room temperature after solution heat treatment. This code indicates the product is in the natural aging phase immediately after solution treatment; it is rarely specified as a final temper without a time period (e.g., W 1/2 hr). |
| T |
Thermally Treated (to produce stable tempers other than F, O, or H) |
Applies to products thermally treated (with or without supplementary strain hardening) to produce stable tempers. The T designation is always followed by one or more Arabic numerals (e.g., T6, T651) indicating specific sequences of heat treatment and/or mechanical working. |
Subdivisions of the H Temper
Subdivisions of the H temper are indicated by two digits (HXX) or, less commonly, three digits (HXXX) following the H.
HXX State (Two digits following H)
(1) The first digit after H indicates the basic treatment process used to obtain the temper:
H1 — Strain-hardened only. Applies to products that are strain-hardened (cold worked) without any supplementary thermal treatment to achieve the required strength level.
H2 — Strain-hardened and partially annealed. Applies to products that are strain-hardened to a level exceeding the desired final strength, then partially annealed (back-annealed) to reduce the strength to the specified level.
For alloys that soften naturally at room temperature (e.g., some 5xxx series), the H2 temper has the same minimum ultimate tensile strength as the corresponding H3 temper.
For other alloys that do not naturally soften, the H2 temper has the same minimum ultimate tensile strength as the corresponding H1 temper, but typically exhibits slightly higher elongation.
H3 — Strain-hardened and stabilized. Applies to products that are strain-hardened and then subjected to a low-temperature thermal stabilization treatment to slightly reduce strength, improve ductility, and stabilize mechanical properties (preventing age-softening at room temperature). The H3 temper applies specifically to alloys which would otherwise age-soften at room temperature unless stabilized (commonly used for 5xxx series alloys containing magnesium).
H4 — Strain-hardened and lacquered or painted. Applies to products that are strain-hardened and subsequently subjected to a lacquering, painting, or coating operation which involves heat that causes some partial annealing, resulting in a final temper similar to H2 but achieved specifically by the coating process.
(2) The second digit after H indicates the degree of strain hardening:
The digit 8 indicates the full-hard or hard temper. The minimum ultimate tensile strength for the HX8 temper is typically specified as the sum of the minimum ultimate tensile strength for the O temper (fully annealed) and a fixed standard strength increment (as defined in relevant specifications, e.g., Table 2 referenced in the original text).
Intermediate states between O (annealed) and HX8 (full-hard) are indicated by digits 1 through 7 following the HX code (e.g., H14 for half-hard, H16 for three-quarter hard). These represent specific, standardized levels of strain hardening.
The digit 9 following the HX code indicates a super-hard or extra-hard temper, with a degree of strain hardening greater than that of the HX8 temper.
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