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Age Hardening

Age Hardening, also referred to as Precipitation Hardening, is a process in which a material is held at temperature to form small, distributed alloy-rich “precipitates”. Before age hardening, a material must be in the solution annealed state where the alloying elements will be supersaturated into a single phase. ​

This treatment increases tensile and yield strength, as well as high-temperature strength in superalloys. It’s an excellent treatment choice for applications in which products will need increased wear resistance, and causes little to no distortion of the part or component.

TMT Equipment/Variations

TMT has air and vacuum furnaces to age parts in. However, depending on the temperature of the process some discoloration can occur when processed in air. Some precipitation hardened stainless steels will also include a cold stabilization (sub-zero) step between solution annealing and aging.

Common Alloys

  • Stainless steels, e.g., 13-8, 15-5, 15-7, 17-4, 17-7
  • Aluminums:
    • 2xx, 3xx, 7xx, 8xx, 2xxx, 6xxx
    • 7xxx: A356, 6061, 7075
  • Copper Alloys: C17000, C17200, C954
  • Superalloys: Monel, Inconel 718
The Retro Engine In Berlin Museum

Applications of age hardening

Stainless steels

Precipitation-hardened stainless steels see much use in corrosive environments where more strength is needed than 300 series stainless steels can provide. Depending on the material grade, they can be hardened up to the mid/low 40s HRC. Aging at higher temperatures will reduce the strength and hardness, but in general increase the corrosion and impact properties. 

They have applications ranging from shafts and gears to medical equipment. One advantage of precipitation-hardened stainless steels is the ability to machine parts in the solution annealed state and then subsequently age the parts to cut down on distortion.

Aluminums

Aluminums are aged to improve their mechanical properties. Peak strength is obtained by aging to the T6 condition, which means that the aluminum alloy product has been given a solution heat treatment followed by quenching, cooling, and aging.

Some alloys will be overaged to the T7 condition to reduce susceptibility to stress corrosion cracking. Aged aluminums see frequent use in aerospace and other applications where high specific strength is needed.

Copper alloys

Precipitation-hardened copper alloys are used when higher strength is needed than can be obtained with typical alloys. Alloying elements, such as Beryllium, are used to increase the hardness. Electrical conductivity will be decreased after age hardening compared to ETP coppers but can have hardness up to 45 HRC. 

Age-hardened copper alloys are often used for bushings, bearings, and small gearings, among other applications.

Associated Specs/Standards

SAE International AMS QQ-A-367 for Aluminum Alloy Forgings as well as AMS:

2759/3, 2770, 2772, 4020, 4021, 4022, 4023 4025, 4026, 4027, 4038, 4039, 4043, 4044, 4045, 4046, 4047, 4048, 4049, 4053, 4078, 4079, 4080, 4082, 4081, 4083, 4115, 4116, 4117, 4122, 4123, 4124, 4127, 4128, 4129, 4139, 4146, 4150, 4154, 4160, 4161, 4167, 4168, 4169, 4170, 4172, 4173, 4676, 5528, 5529, 5568, 5604, 5644, 5617, 5622, 5643, 5659, 5673, 5678, 5824, 5825, 6532, 6875, 7199

ASTM A313, A510, A564, A579, A693, A705, B209, B210, B211, B221, B234, B241, B247, B308, B313, B316, B345, B404, B429, B483, B457, B549, B632, B808

ASME SA564, SA693, SA705

MIL 1684

SAE J454, J467

What To Consider When Specifying Heat Treatment

  • Material
  • Aged Condition
  • Furnace Atmosphere
  • Hardness (if required)
  • Mechanical Testing (if required)
  • Specification (if required)

Have more technical questions?

Don’t hesitate to contact a TMT engineer here. Thermal Modification Technologies has years of heat-treating experience and we’re happy to answer any of your questions.