Aluminium Numbering System

Aluminium 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 aluminium grades. To help make sense of all these combinations, an aluminium 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 aluminium alloys. First, it is important to know whether the aluminium alloy is wrought or cast.

Wrought Aluminium

Wrought aluminium 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 aluminium alloy, whereas a 6XXX alloy indicates that significant amounts of magnesium and silicon have been added to the aluminium. Below is a table for the different alloying elements of wrought aluminium:

 
The second digit in the wrought aluminium 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 aluminium designation system are used to label the specific alloy. These numbers are arbitrary except for the 1XXX series of aluminium. In the 1XXX series, the last two digits specify the minimum aluminium content between 99% and 100%. For example, 1060 aluminium would have a minimum pure aluminium content of 99.60%.

Cast Aluminium

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

 
The second and third digits of the cast aluminium numbering system are also arbitrary; indicating the aluminium alloy, with the exception of the 1XX.X series. Similar to the wrought aluminium alloy designation system, the second and third digits for these grades are used to indicate aluminium purity above 99%. The final digit after the decimal point is used to mark whether the aluminium 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 aluminium alloys. These distinguish what processing has been done to the aluminium 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 aluminium alloy, the “T” indicates that the aluminium 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 aluminium 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 aluminium alloys are heat treatable. The exception to this is some of the 4XXX series aluminium alloys are unresponsive to heat treatment.