How to Specify a Temper When Choosing an Aluminium Alloy

Since the properties of aluminium alloys are so influenced by work hardening and heat treatment, the temper (strengthening treatment, if any) must be designated in addition to the composition code. This designation is attached to the preceding four-digit number, separated from it by a hyphen, to indicate the treatment or absence thereof; for example, 6082-T651. Of course, temper treatments that specify strain hardening do not apply to the cast alloys.

Aluminium Extrusions


As fabricated – no special treatment.


Strain hardened (wrought aluminium). H is followed by two digits, the first indicating a heat treatment, if any; and the second indicating the degree of work hardening remaining; for example:

  • H1X – No heat treatment after strain hardening, and X = 1 to 9, indicating degree of work hardening;
  • H2X – Partially annealed, and X = degree of work hardening remaining in product;
  • H3X – Stabilised, and X = degree of work hardening remaining. Stabilised means heating to slightly above the service temperature anticipated.


Annealed to relieve strain hardening and improve ductility; reduces strength to lowest level.


Thermal treatment to produce stable tempers other than F, H, or O. It is followed by a digit to indicate specific treatments; for example:

  • T1 – cooled from elevated temperature, naturally aged;
  • T2 – cooled from elevated temperature, cold worked, naturally aged;
  • T3 – solution heat treated, cold worked, naturally aged;
  • T4 – solution heat treated and naturally aged;
  • T5 – cooled from elevated temperature, artificially aged;
  • T6 – solution heat treated and artificially aged;
  • T7 – solution heat treated and overaged or stabilised;
  • T8 – solution heat treated, cold worked, artificially aged;
  • T9 – solution heat treated, artificially aged, and cold worked;
  • T10 – cooled from elevated temperature, cold worked, and artificially aged.


Solution heat treatment, applied to alloys that age harden in service; it is an unstable temper.

At CNC Proto we specialise in the machining of non-ferrous metals, mostly 6000 and 7000 series aluminium alloys, and engineering plastics. You can see a list of our most used alloys in our Services page. If your parts require a specific aluminium alloy other than the ones listed, feel free to let us know on our Quote Request form!

For more articles on CNC machining, materials and design of machined parts, be sure to check our Resource Library.


Fernando Duarte Ramos

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With an MSc. in Mechanical Engineering, Fernando has worked 8 years at CERN designing and building the next generation of particle detectors alongside top European engineers and physicists. Being passionate about CNC machining, he started CNC Proto, an online CNC machining service in Europe dedicated to providing fast turnaround, high quality parts at a competitive cost. Learn more About Us

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