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Where Do Those "AA" Designations Come From?
12-12-02
Identified by colors from an alternative rainbow, the AA Registration Record Series provide some of the most basic product specifications for materials in the aluminum industry. With the Aluminum Association's publication in October 2002 of the revised "Teal Sheets" (a.k.a. the International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys), it's a good time to take a look at the source of the designations that are used every day.
In the first half of the 20th century, aluminum alloy development was underway on a number of fronts, and the resulting alloys had names like 2S, 24S and 75S as well as a variety of trade names and company-specific designations. The modern aluminum alloy designation system, at least for wrought aluminum and wrought aluminum alloys, had its beginnings in 1954 when the Aluminum Association developed a 4-digit alloy designation system to address the need for a uniform system adequate for use by all. This system was later approved by the American National Standards Institute in the form of American National Standard H35.1, which was later expanded to also include the Association's Temper Designation System. In 1970, the alloy designation system was adopted internationally, and currently 24 regional and national aluminum organizations have agreed to use the Aluminum Association designation system for wrought alloys and to have their alloys registered with the Aluminum Association.
The assignment of a number designation to an alloy composition follows a well-defined set of rules that are administered by the Aluminum Association's Technical Committee on Product Standards. For the wrought alloys, a 4-digit designation system is used in which the first digit is assigned based on the major alloying element(s). The last two digits in the 1xxx series used for alloys in which aluminum is 99.00% or greater reflect the minimum aluminum percentage above 99.00%, while in the 2xxx-8xxx families the last two digits have no special significance but serve only to identify the different aluminum alloys within the group. The second digit, if other than "0", denotes modifications in composition to the original alloy. Finally, the designation system provides for "national variations" of an alloy, in which the composition limits are similar but not identical to those registered by another country. These national variations are designated by a serial letter starting with "A "after the numerical designation.
Wrought alloys that have been registered with the Aluminum Association are contained in the International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys. Prior to 1998, there were two registration records for wrought alloys, that for North America (the "Green Sheets") and a separate international registration (the "Blue Sheets"). In 1998, these two documents (and their associated colors) were integrated into the current single international registration record, popularly known as the "Teal Sheets" by virtue of the color of paper upon which it's printed. This publication also contains additional information related to alloy densities, inactive alloy designations, and cross references of the international designations to ISO alloy designations.
The Teal Sheets are but one member of the colorful family of the Registration Record Series. Here are the others, along with some helpful comments:
- Designations and Chemical Composition Limits for Aluminum Alloys in the Form of Castings and Ingot (Pink Sheets)-Also covered under ANSI H35.1, this publication contains information on composition limits for castings and ingot. The designation system is different than for wrought alloys, consisting of three digits for composition, followed by a period and then another digit to indicate product form (ingot or casting). Alloy modifications are handled with a serial letter appearing at the front of the numerical designation. There is no international accord regarding casting and ingot designations, meaning that alternative systems are often used outside of the U.S.
- Designations and Chemical Composition Limits for Aluminum Hardeners (Gray Sheets)-Covered by ANSI H35.3, the registration record contains registered limits for aluminum hardeners including master alloys as well as cast grain refiners and modifiers. These are designated by four digits prefixed by the letter "H". The first two digits identify the hardener alloy group by major alloying element, while the last two digits indicate the sequential registration of hardener alloys. They are covered under an international accord and an international registration record is being developed.
- International Designations and Chemical Composition Limits for Unalloyed Aluminum (Gold Sheets)-According to ANSI H35.4, these designations cover unalloyed aluminum not made by a refining process and used primarily for remelting. The system is again a four digit one, with a "P" prefix and a serial letter suffix. In between, the first two digits indicate the first two digits to the right of the decimal place for maximum silicon, and the last two digits similarly for iron. The basic unalloyed designation can be followed by the letter "A", with variations designated by serial letters replacing the A. These designations are also covered under international accord.
- Tempers for Aluminum and Aluminum Alloy Products (Yellow Sheets) and -Metric Edition (Tan Sheets)- Temper designations are also defined in ANSI H35.1, mentioned earlier. Temper designations by themselves define generic production processes and, when used in combination with an alloy designation and product form, additionally define registered mechanical properties and characteristics for that product. The basic temper designations of F, O, T, W, and H are based on the generic process descriptions. The addition of subsequent digits to these basic designations, where applicable, denotes specific subdivisions of the basic temper and variations. The temper designation and registration systems are domestic only; there is no international accord for tempers.
While this all seems very orderly, it is not infrequent that an aluminum alloy
is designated by some system other than the Aluminum Association system. This
may occur when the alloy is identified by a tradename, is older, or may have been
developed outside the U.S. When that is the case, it is useful to be able to determine
the alloy's composition and perhaps an Aluminum Association equivalent. Alloy
cross-references are a useful resource in these cases, and two that are available
are the Worldwide Guide to Equivalent Nonferrous Metals and Alloys, 4th Edition,
available from ASM International (www.asminternational.org)
and Key to Aluminium Alloys, 5th Edition, by Dr. John Datta, published by Aluminium-Verlag
in Germany and available through ASTM International (www.astm.org).
In this short overview it is impossible to cover all of the important details
and procedures related to the Aluminum Association's alloy and temper designation
systems. A more thorough discussion of this topic including the registration process
as it applies to wrought alloys is given in a recently published article by Peter
Pollak and Parvaneh Shafiee of the Aluminum Association entitled "Enabling Communications
Pertaining to Aluminum Mill Products Through Industry Standards", and published
by TMS (www.tms.org) in Aluminum
2002, edited by Subodh K. Das and Michael H. Skillingberg.
The registration record Series described above is available from the Aluminum Association Bookstore online at www.aluminum.org or by calling (301) 645-0756. Just ask for your favorite color!
Article courtesy of Secat, Inc. - Research Resource for the Aluminum Industry
www.secat.net
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