Aluminum readily forms alloys with a wide range of other elements, from lithium to lead.
The most commonly-encountered system for identifying aluminum alloys is that of the Aluminum Association. Commercially-available alloys are assigned a four-digit number, followed by a hyphen, a letter and, often, one to three numerals identifying treatment. For example, 6061-@@
The designations provide some clues to the composition of the alloy, but they are not a complete description of its constituents or their proportions. That is contained in the standard for the alloy, which is maintained by the Aluminum Association, who act as the international registrar.
The first digit of the four-digit number classifies the alloys by the principal alloying element:
|Grade||Major alloying element||Strength||Temper||Effect|
|1xxx||at least 99% aluminum by weight.||weak||H||excellent corrosion resistance and thermal and electrical conductivity|
|3xxx||manganese||medium||H||good workability. welds well.|
|6xxx||magnesium and silicon||medium||T||good corr|
|8xxx||some other element(s)||H/T|
A decimal point between the third and fourth digits indicates a casting alloy.
|Grade||Major alloying element||Strength||Effect|
|1xx.x||at least 99% aluminum by weight.||weak||excellent corrosion resistance and thermal and electrical conductivity|
|3xx.x||silicon, with copper and/or magnesium|
The second digit is used to distinguish later revisions of the specification for that alloy, except for the 1xxx group, where 10xx indicates unalloyed aluminum, having only naturally-occurring impurities, and any other digit in the second place has been assigned a meaning having to do with control of particular impurities.
In the 1xxx group, the last two digits indicate the minimum percentage of the 1% of the alloy that need not be aluminum, that must be aluminum. “1350,” say, is at least 99.50% aluminum. In all the other groups, the last two digits are not a “hot code;” they simply identify a particular alloy.
To convert a 4-digit designation to the UNS system, prefix “UNS A9” to it. So for example 6061 becomes UNS A96061. To convert a 4-digit wrought alloy designation to EN 573, prefix “EN AW.” So 5754-O becomes EN AW-5754-O. These steps can be reversed to get 4-digit designations.
Some examples of alloy designations, with typical uses:
|2219||rocket fuel tanks (strong when cold). Also used in high temperature environments.|
|3004||beverage can bodies|
|390.0||automobile engines (cylinder blocks) Note decimal point indicating a casting alloy.|
|5182||beverage can tops|
|7050||strong, with great resistance to stress cracking corrosion. wide use in air- and spacecraft.|
|7075||another aerospace alloy|
A system substantially the same as the present system of temper designations was adopted in October 1947. Previously also made use of letters and numbers, e.g., .
|F||As fabricated. No treatment at all.|
|O||Heat treated to the temper with the lowest strength.
Sometimes the heat treatment is not some additional, separate, process,
but an aspect of the fabrication. If that leads to the desired
low-strength annealed state, the O designation is appropriate.
O may be followed by a digit to indicate some special characteristic, but it usually isn't.
|H||Strain hardened wrought products. May be heat-treated to reduce strength. "H" is always followed by two or more digits.|
|W||Heat treated, but left in an unstable state which will change as it ages at room temperature.|
|T||Heat treated to produce a stable temper other than F, O or H. "T" is always followed by one or more digits.|
The T temper designations apply to alloys in the 2xxx, 6xxx and 7xxx groups, with a few oddballs elsewhere (lithium alloys aerospace) 2090 8090
|T1||Cooled from a high-temperature shaping process and then naturally aged until stable.|
|T2||Cooled from a high-temperature shaping process, cold-worked, and then naturally aged until stable.|
|T3||Heated to the temperature at which some of the constituents go into solution, cold worked, and then naturally aged until stable|
|T4||Heated to the temperature at which some of the constituents go into solution, and then naturally aged until stable.|
|T5||Cooled from a high-temperature shaping process and then artificially aged until stable.|
|T6||Cooled from a high-temperature shaping process and then artificially aged.|
|T7||Heated to a temperature at which some of the constituents go into solution, and artificially overaged|
|T8||Heated to a temperature at which some of the constituents go into solution, cold worked, and artificially aged.|
|T9||Heated to a temperature at which some of the constituents go into solution, artificially aged, then cold worked.|
|T10||Cooled from a high-temperature shaping process, cold worked, and then artificially aged|
Some alloys were given proper names by their inventors or the firms marketing them.
In the ASTM-ASME system, discontinued for wrought alloys in the 1950's and for cast alloys in 1974, each constituent was assigned a letter.
An alloy was identified by giving the two letters for the most prevalent constituents, in the order of their concentration, followed by their concentrations, in the same order, as percentages each rounded to a whole number. So, for example, what we call 6151, with 0.80% silicon and 0.63% magnesium, would be SG11. Unfortunately present-day 6066, with 1.35% silicon and 1.1% magnesium, would also be SG11. In these situations letters were added to the end to distinguish the two: SG11A and SG11B.
Pure aluminum by a numeral, the purity in tens of a percent, but omitting the decimal point. For example "995" would be 99.5% aluminum.
The SAE adopted the AA designation system in 1990.
In the Commercial System, two digits followed by the suffix S. This system influenced the AA system; the meaning of the initial digits are very similar (e.g., c is for copper, and so on.).
ANSI H35.1/H35.1M-2013. American National Standard Alloy and Temper Designation Systems for Aluminum.
ASTM B 211-03. Standard Specification for Aluminum and Alumnum-Alloy Bar, Rod, and Wire.
ASTM B 918 Practice for Heat Treatment of Wrought Aluminum Alloys.
ASTM E 527. Practice for Numbering Metals and Alloys (UNS)
SAE J452, J453
You can get quite a bit of data on an alloy, not including tempering, by converting its 4-digit designation to a UNS number and looking it up on MatWeb:
An engineer at the Federal Aviation Administration has compiled an unofficial cross reference between current and obsolete alloy designations, to support those trying to keep antique aircraft flying. Many valuable tables comparing, for example, old commercial, ASTM-ASME and SAE designations with current ones.
Former alloy and temper designations, aluminum and magnesium alloys.
ANM-112N-06-04 (25 September 2006)
Download from https://www.faa.gov/aircraft/air_cert/design_approvals/csta/publications/media/formerdesignations.pdf
These are summarized in a pair of articles by Joseph C. Benedyk:
International temper designation systems for wrought aluminum alloys. Part I — Strain hardenable (H temper) aluminum alloys.
Light Metal Age, vol. 67, no. 5 (October 2009), pages 26-30.
See table III on page 29.
International temper designation systems for wrought aluminum alloys. Part II — Thermally treated (T temper) aluminum alloys.
Light Metal Age, vol. 68, no 4 (August 2010), pages 16-22.
See table VI on page 22. The article includes (table V) an extensive list of Tn designations, including not only those from ANSI H35.1, but also EN 515 and ISO 2107 standards, with helpful explanations.
Aluminum Standards and Data 2013.
Arlington, VA: The Aluminum Association, 2013.
Various editions in different formats: online, CD, etc..
Werner Hesse, editor.
Aluminium-Schüssel = Key to Aluminium Alloys, 10th edition.
Berlin: Beuth, 2012.
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Last revised: 3 May 2014.