Precipitation or Age Hardening

  • Some metals when quenched from a high temperature (solution treatment temperature) are essentially in their softest state after quenching but have the ability to be subsequently hardened by relatively low temperature treatments, generically referred to as precipitation or age hardening.
  • Precipitation Hardening is applied to treatments carried out at elevated temperature, typically ranging from 100° to 200°C for some aluminium alloys to over 700° C for some stainless steels and higher alloyed steels/nickel alloys. Times required at the precipitation temperature can vary from 4 to 30 plus hours.
  • Age Hardening is applicable to some aluminium alloys (and occasionally some other non-ferrous metals) where the hardening occurs on holding at ambient/room temperature for many hours.  Material required to remain soft for intermediate processing may be held at sub-zero temperature to prevent aging.
  • Relatively low distortion during heat treatment.
  • Increases yield and tensile strength of most materials.
  • Increases through hardness.
  • Enables easier bulk machining to be carried out in the soft solution treated condition, followed by a relatively simple low temperature age/precipitation treatment.
  • Some titanium and special copper alloys may also respond to precipitation treatments.  Some stainless steels may receive a two or more stage precipitation heat treatment aimed at producing specific combinations of mechanical and corrosion properties.
  • Typical materials that can be precipitation hardened:
    1. Aluminium alloys – 2000, 6000, 7000 series, (not all alloys in the series)
    2. Stainless steels – 17/4 PH. 17/7 PH, FV520B (BS – S143 – 5)
    3. Maraging steels – DTD 5212, 5232, 18Ni 200 / 250 / 300, 1.2709.
    4. Copper alloys – copper-beryllium, specialised “Spinodal” alloys (C17000, C18000, C94000 series)
    5. Titanium alloys – 6Al4V, 6Al6V2Sn (alpha-beta alloys usually)
    6. Electroless Phosphor-Nickel plating – a nickel plating with hardness over 700 HV.
  • Electric air circulating vertical pit furnaces up to 1730mm deep x 1120mm diameter are capable of handling total loads up to a maximum 2000kg.

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