Aluminium grades

**from ^ **

**Alloy Composition/Designation **

Aluminum alloy composition designations, in the United Sates, are made under the guidance of the Aluminum Association. The major aluminum producers have agreed upon a four digit numerical system for designating specifically the composition of wrought aluminum and aluminum alloys, while a three digit system is used for casting aluminum alloys. The first of the four digits in the alloy number indicates the alloy group which identifies the primary alloying element or elements within the alloy. The 1XXX group is at least 99% pure aluminum
The 2XXX group is alloyed primarily with Copper, which is added for higher strength but reduces the corrosion resistance
The 3XXX group is alloyed primarily with Manganese, for moderate strength
The 4XXX group is alloyed primarily with some Silicon to lower the melting point and increase fluidity for casting
The 5XXX group is alloyed primarily with Magnesium to make a moderate strength alloy
The 6XXX group is alloyed primarily with both Magnesium and Silicon to make a moderate strength alloy
The 7XXX group is alloyed primarily with Zinc to make a high strength alloy.
The 8XXX group is used to indicate an alloy whose primary alloy element is other than those above
The 9XXX group has not so far been used or assigned, but with the cold war over it wouldn't be surprising to find that the defense industry may have privately had something in the 9XXX group held secret
In the alloys designated from the 2XXX to the 7XXX group, the last two digits identify the uniquely different alloys in the series. As new alloys become commercially available, the last two digits are assigned consecutively beginning with XX01, (wouldn't you think they would be running short on these by now?). The two digits bring with them a specific chemical composition range, which must be adhered to.
The second digit indicates any modifications in the composition of the original alloy used. If the second digit is "0", zero, there have been no modifications made to the original assigned and designated alloy. If modifications are made to the original alloy, integers 1 to 9, which are assigned consecutively, are used to indicate the modification, and note commonly its existence. New, experimental aluminum alloys are grouped with the appropriate 1XXX to 9XXX series above but are prefixed with an "X". The "X" is discontinued when the alloy becomes standard. Do not make the mistake of believing that a higher alloy designation number means the aluminum alloy is stronger, harder, or more resistant to failure. Sometimes that is true but the alloy's temper also says something about its strength, and hardness.