Metals Codes - 6: Aluminum Codes
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.

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

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
The closest UNS conversion for IADS aluminum follows the information above. The UNS system uses the first digit "9" to differentiate wrought aluminum from cast aluminum. So an IADS 6061 aluminum would be UNS A96061. However there is no room in the UNS system for traditional temper tags such as IADS 6060-T6. It remains to be seen how new UNS standards will address this. It is this authors assumption that the normal addendum will be used such as A96061-T6.
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label: standards, UNS, AISI,ASTM, ASE, coding, steel, stainless steel, tool steel, aluminum, copper, austenetic, martensitic, ferritic, precipitatin hardening