The Aluminium Numbering SystemShea Bethell
What is the Aluminium Numbering System?
Aluminium is usually alloyed with several other elements in order to improve various properties such machinability or chemical resistance. As a result, there is a large amount of combinations of various alloying elements that can be combined to achieve the desired properties, this results in a wide variety of aluminium types or grades. To help keep track of all the combinations, an aluminium numbering system is utilised.
The Aluminium Association created the nomenclature and it is the organisation that maintains this designation system that is used internationally. There are many rules for labeling the various types of aluminium alloys. It is important to first know whether the aluminium alloy is wrought or cast. In this article we will focus on wrought aluminium alloys and the numbering system used to identify them.
Wrought aluminium alloys use a standard 4-digit numbering system. The first digit designates the primary alloying element in the aluminium alloy. An example would be the 1XXX alloy indicating a mostly pure aluminium alloy, whereas a 6XXX alloy would indicate that significant amounts of magnesium (Mg) and silicon (Si) have been added to the aluminium. Below is a useful table detailing the different alloying elements of used in wrought aluminium:
|1xxx|| Pure Aluminium|
|6xxx|| Magnesium and Silicon|
The second digit in the above wrought aluminium numbering system would indicate if 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 last two digits in the above wrought alloy aluminium designation system are used to label and differentiate the specific alloys. These numbers are completely arbitrary except when used in the 1XXX series of aluminium. In the 1XXX series, the last two digits specify the minimum aluminium content between 99% and 100%. As an example, 1050 aluminium would have a minimum pure aluminium content of 99.50%.
Cast aluminium alloys use a similar numbering system except with 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.
Temper designations distinguish what processing has been done to the aluminium to increase mechanical properties such as tensile strength and hardness. These designations can follow the digits for both wrought and cast aluminium alloys.
- F – The “F” designation indicates the alloy is fabricated, and no special processing has been used to increase the alloys mechanical properties.
- H – The “H” designation indicates the alloy has been strain hardened.
- O – The “O” designation indicates the alloy is an annealed aluminium alloy.
- T – The “T” designation indicates that the aluminium alloy has undergone thermal treatment.
- W – The “W” designation indicates thermal heat treatment has taken place.
Only the 2XXX, 4XXX, 6XXX, and 7XXX series of wrought aluminium alloys are heat treatable. The exception to this is that some of the 4XXX series aluminium alloys are unresponsive to heat treatment.