Aluminum is normally alloyed with several different elements in order to improve the mechanical or chemical properties. As a result, there are a large number of combinations of alloying elements that can be used to achieve the desired properties, resulting in a wide variety of aluminum grades. To help make sense of all these combinations, an aluminum numbering system is used.

The Aluminum Association created the nomenclature and it is the organization that maintains the designation system. There are many different rules for labeling the various types of aluminum alloys. First, it is important to know whether the aluminum alloy is wrought or cast.

Wrought Aluminum

Wrought aluminum alloys use a 4-digit system. The first digit is used to designate the primary alloying element. As an example, a 1XXX alloy indicates a mostly pure aluminum alloy, whereas a 6XXX alloy indicates that significant amounts of magnesium and silicon have been added to the aluminum. Below is a table for the different alloying elements of wrought aluminum:

1xxx   Pure Aluminum
2xxx   Copper
3xxx   Manganese
4xxx   Silicon
5xxx   Magnesium
6xxx   Magnesium and Silicon
7xxx   Zinc
8xxx   Other

 
The second digit in the wrought aluminum numbering system indicates that there has been a special modification to one of the alloying elements. These controls are registered with IADS and require the specific IADS documentation. The third and fourth digits in the wrought alloy aluminum designation system are used to label the specific alloy. These numbers are arbitrary except for the 1XXX series of aluminum. In the 1XXX series, the last two digits specify the minimum aluminum content between 99% and 100%. For example, 1060 aluminum would have a minimum pure aluminum content of 99.60%.

Cast Aluminum

Cast aluminum alloys use a 4 digit system but includes a decimal point (XXX.X). Similar to wrought aluminum, the first digit in the cast aluminum alloy designation system indicates the major alloying element or elements. The table below features the different alloying elements assigned to each digit:

1xx.x   Pure Aluminum
2xx.x   Copper
3xx.x   Silicon and/or Copper and/or Magnesium
4xx.x   Silicon
5xx.x   Magnesium
6xx.x   Not used
7xx.x   Zinc
8xx.x   Tin
9xx.x   Other

 
The second and third digits of the cast aluminum numbering system are also arbitrary; indicating the aluminum alloy, with the exception of the 1XX.X series. Similar to the wrought aluminum alloy designation system, the second and third digits for these grades are used to indicate aluminum purity above 99%. The final digit after the decimal point is used to mark whether the aluminum alloy is a casting or an ingot. A “0” indicates a casting while “1” indicates an ingot.

Temper designations can follow the digits for both wrought and cast aluminum alloys. These distinguish what processing has been done to the aluminum to increase mechanical properties such as tensile strength and hardness. For example, the “F” designation indicates fabricated; in other words, no special processing has been used to increase mechanical properties. The “H” designation means strain hardened, the “O” designates an annealed aluminum alloy, the “T” indicates that the aluminum alloy has undergone thermal treatment, and the “W” designates thermal heat treating. It is important to take note of these thermal designations when subjecting the aluminum alloy to processes that create enough heat to alter the heat treatment or strain hardening. Only the 2XXX, 4XXX, 6XXX, 7XXX, 2XX.X, 3XX.X, 4XX.X and 7XX.X series of aluminum alloys are heat treatable. The exception to this is some of the 4XXX series aluminum alloys are unresponsive to heat treatment.

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