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Wrought Aluminium Alloys

Until 1970, designations of wrought aluminium alloys were a mess; in many countries, they were simply numbered in the order of their development. The International Alloy Designation System (IADS), introduced in 1970 and now widely accepted, uses a classification developed by the Aluminium Association of the United States. It works as follows.

The IADS gives each wrought alloy a 4-digit number. The first digit indicates the major alloying element or elements, as shown in the table below. Thus the series 1xxx describe unalloyed aluminiums; the 2xxx series contain copper as the major alloying element, and so forth.

Series Major Alloying Elements
1xxx 99% Aluminium
2xxx Copper
3xxx Manganese
4xxx Silicon
5xxx Magnesium
6xxx Magnesium and Silicon
7xxx Zinc
8xxx Other (including Lithium)

Table 1 IADS Terminology for Wrought Aluminium Alloys

The third and fourth digits are significant in the 1xxx series but not in the others. In the 1xxx series the last two digits describe the minimum purity of the aluminium; thus 1145 has a minimum purity of 99.45%; 1200 has a minimum purity of 99.00%. In all other series, the third and fourth digits are simply serial numbers; thus 5082 and 5083 are two distinct aluminium-magnesium alloys. The second digit has a curious function: it indicates a close relationship: thus 5352 is closely related to 5052 and 5252; and 7075 and 7475 differ only slightly in composition.

To these serial numbers are added a suffix indicating the state of hardening or heat treatment. The suffix F means "as fabricated". Suffix O means "annealed wrought products". The suffix H means that the material is "cold worked". The suffix T means that it has been "heat treated".

Cast Aluminium Alloys

No classification system for cast aluminium alloys has international acceptance. That of the Aluminium Association of the United States (AAUS) is the most widely used. As with wrought alloys, the first digit indicates the alloy group, as shown in the table below.

New Series Old Series Major Alloying Element
1xx.x - > 99% Aluminium
2xx.x 1xx Copper
3xx.x 3xx Silicon, Copper and/or Magnesium
4xx.x 1 to 99 Silicon
5xx.x 2xx Magnesium
6xx.x - Unused
7xx.x 6xx Zinc
8xx.x 7xx Tin
9xx.x - Other

Table 2 AAUS Terminology for Cast Aluminium Alloys

In the 1xx.x group, the second two digits indicate the minimum percentage of aluminium; thus 150.x indicates a composition containing a minimum of 99.5% aluminium. The digit to the right of the decimal point indicates the product form: 0 means "castings" and 1 means "ingot". In the 2xx.x to 9xx.x groups, the second two digits are simply serial numbers. The digit to the right of the decimal point again indicates product form.

Magnesium Alloys

No classification system for magnesium alloys has international acceptance. That of the American Society for Testing Materials (ASTM) is the most widely used. In this system, the first two letters indicate the principal alloying elements as shown in the table below. The letter corresponding to the element present in the greatest quantity is used first; if they are equal, they are listed alphabetically. The letters are followed by numbers which represent the nominal compositions of the principal alloying elements in weight% rounded to the nearest whole number; thus AZ91 means the alloy Mg-9Al-1Zn.

Series Major Alloying Element
A Aluminium
B Bismuth
C Copper
D Cadmium
E Rare earths
F Iron
G Magnesium
N Nickel
P Lead
Q Silver
R Chromium
S Silicon
T Tin
Y Antimony
Z Zinc

Table 3 ASTM Terminology for Magnesium Alloys

Titanium Alloys

There are four groups of titanium alloys: a alloys, near-a alloys, a + b alloys and b alloys. A designation system with some logic to it simply lists the quantities of the principal alloying additions; thus "Ti-8-1-1" contains 8% aluminium, 1% molybdenum and 1% vanadium; and "Ti-6-4" means 6% aluminium and 4% vanadium. In parallel with this, the IMI numbering system is still widely used. The IMI number gives no clue to the composition. The table below lists the designations of the more widely used alloys.


Alloy types

CP Ti 99.5; IMI—115; Ti 35A  
CP Ti 99.0; IMI—155; Ti 75A  
IMI—260 a Alloys
IMI—685 near—a Alloys
Ti—6—4; IMI—318  
Ti—6—6—2 ab Alloys
Ti—8 Mn  
Beta 111  
Ti—8—8—2—3 b Alloys
Transage 129  
Beta C  

Table 4 Designations and equivalents of Titanium Alloys