Definition - What does Precipitation Hardening mean?
Precipitation hardening is a method that makes use of heat application to a pliable material, like metal alloy, to make it tougher. This technique gives strength to alloys by hardening them and adding fine, solid impurities known as precipitates. This can halt dislocation movements within the structure of its crystal lattice.
Dislocations are the main cause of material plasticity. Hence, eliminating dislocations can also improve the yield strength of materials. The most common alloys used in this technique include:
Precipitation hardening is also known as age hardening.
Corrosionpedia explains Precipitation Hardening
The process of precipitating solid materials begins with heating to extremely elevated temperatures to achieve dissolution. This process can last for as short as an hour to a maximum of 20 hours before the precipitate is completely dissolved. The mixture produced can be highly saturated and can be readily subjected to treatment.
The solution’s high saturation, or supersaturation, is obtained by quenching. This can be accomplished in air or water, or the mixture of these two. It is a vital step in strengthening solution, as it prepares the material for the succeeding step of hardening precipitation.
Once the quenching phase has been completed and the solution has undergone aging, artificial aging takes place. This can be accomplished by subjecting the solution to elevated temperatures. Afterward, the solution undergoes soaking for two to 20 hours. The time for soaking combined with the aging temperature is identified by the intended strength required for the product.
Precision is essential when calculating the time and temperature. Excessive soaking or temperatures can result in reduced precipitates, which can promote high ductility and less strength. Another way to achieve precipitate hardening is through natural aging. However, this consumes more time—from days to weeks.
Impurities that are built via the precipitation or hardening technique can cause disruption to the crystal lattice structure in aluminum, stainless steel and other types of alloys. These prevent dislocations, making it difficult for lose particles to cut through the material.
Precipitation hardening is commonly used for fabricating parts that must withstand extremely high temperatures, such as turbo chargers and pressure vessels. Additionally, it is used on alloys like copper that can be used for roofing, building ships and many other applications.