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.
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
H Strain Hardening
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
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