Dr. Dmitri Kopeliovich
Precipitation hardening (age hardening) – strengthening by precipitation of fine particles of a second phase from a supersaturated solid solution.
The precipitation hardening heat treatment involves the following stages:
The part is held at this temperature for a time varying from 1hour to 20 hrs. until the dissolving has been accomplished.
Quenching is carried out in water, water-air mixture or sometimes in air.
Object of the quenching operation is obtaining supersaturation solid solution at room temperature.
Depending on the temperature at which this operation is carried out aging may be artificial or natural.
At this stage the part is heated up to a temperature below the solvus temperature, followed by soaking for a time varying between 2 to 20 hours.
The soaking time depends on the aging temperature (the higher the temperature, the lower the soaking time).
Too high aging temperature and time result in overaging – decrease of the strength and increase of ductility.
Natural aging is conducted at room temperature and it takes a relatively long period of time (from several days to several weeks).
Precipitation hardening heat treatment is commonly used for the following alloys: