Alloy Designations

Aluminum casting alloys in the U.S. are numbered according to a three-digit (plus decimal) system adopted by the Aluminum Assn. (AA) in 1954 and approved by the American National Standards Institute in 1957 (ANSI H35.1). The American Society for Testing and Materials (ASTM), the Society of Automotive Engineers (SAE), and the Federal and Military specifications for aluminum castings conform to the AA designation system.
Table 1. Aluminum Alloy Classification System
In this system, major alloying elements and certain combinations of elements are indicated by the number series in Table 1. The 6XX.X and 9XX.X series are not currently in use, but they are being held open for possible use in the future. The digit following the decimal in each alloy number indicates the form of product:
• a “0” (zero) following the decimal indicates the chemistry limits applied to an alloy casting;
• a “1” (one) following the decimal indicates the chemistry limits for ingot used to make the alloy casting;
• a “2” (two) following the decimal also indicates ingot but with somewhat different chemical limits (typically tighter, but still within the limits for ingot).
Generally, the XXX.1 ingot version can be supplied as a secondary product (remelted from scrap, etc.), whereas the XXX.2 ingot version is made from primary aluminum (reduction cell).
Some alloy names include a letter. Such letters, which precede an alloy number, distinguish between alloys that differ only slightly in percentages of impurities or minor alloying elements (for example, 356.0, A356.0, B356.0 and F356.0).

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