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.
Key to the IADS aluminum numbering system
.
The first digit designates the major alloy
- The digit "1" as in 1xxx designates alloy free (no alloys) and is at least 99% aluminum.
- The digit "2" as in 2xxx designates copper as the major alloy
- The digit "3" as in 3xxx designates manganese as the major alloy
- The digit "4" as in 4xxx designates silicon as the major alloy
- The digit "5" as in 5xxx designates magnesium as the major alloy
- The digit "6" as in 6xxx designates magnesium and silicon as the major alloys
- The digit "7" as in 7xxx designates zinc as the major alloy
- The digit "8" as in 8xxx designates an unspecified alloy (including lithium)
The second digit designates the purity of the aluminum and mill control
- The digit "0" designates no control
- The digits "1" through "9" designates different control levels at the mill. These controls are registered wtih IADS. A complete understating requires an in depth study of the specific IADS documentation
The third and fourth digits have two meanings.
- If the aluminum is 1xxx then the last two digits designate the amount of aluminum above 99%. For example 1025 signifies a non alloyed aluminum that is 99.25% pure aluminum with the remaining 0.75% uncontrolled impurities
- If the aluminum is any other than 1xxx the last two digits are registered wtih IADS and are not otherwise meaningful. A complete understanding requires an in-depth study of the specific IADS documentation.
The treating of aluminum after it is milled sometimes called temper) is designated by a letter following the four digit IADS number. Each letter signifies exactly how the aluminum
was treated. Not all treating is heat treating and not all treating affects temper.
F as fabricated, no digits appended
W solution heat treated, no digits appended
O Annealed, no digits appended
- H1 Strained hardened only
- H2 Strain Hardened and annealed
- H3 Strain Hardened and stabilized thermally
- An additional digit may follow which designates hardness
- H__2 quarter hard
- H__4 half hard
- H__6 three quarter hard
- H__8 fill hard
Example: 3040-H41 would signify a treating of strain hardening to half hard.
T Thermally treated
- T1 Cooled from hot work an naturally aged
- T2 Annealed
- T3 Solution treated and cold worked
- T4 Solution treated and naturally aged
- T5 Cooled from hot work and furnace aged
- T6 Solution treated and furnace aged
- T7 Solution treated and stabilized
- T8 Solution treated, cold worked, and furnace aged
- T9 Solution treated, furnace aged, and cold worked
- T10 Cooled from temperature, furnace aged, and cold worked
- T51 Stress relieved by stretching
- T510 Stress relieved by stretching with no further processing
- T511 Stress relieved by stretching and minor straightening
- T52 Stress relieved by compression
- T54 Stress relieved stretching and compression
- T42 Solution treated from O or F temper and naturally aged
- T62 Solution treated from O or F