Tempering - Precipitation Hardening Alloys

Precipitation Hardening Alloys

Precipitation hardening alloys first came into use during the early 1900s. Most heat-treatable alloys fall into the category of precipitation hardening alloys, including alloys of aluminum, magnesium, titanium and nickel. Several high-alloy steels are also precipitation hardening alloys. These alloys become softer than normal when quenched, and then harden over time. For this reason, precipitation hardening is often referred to as "aging."

Although most precipitation hardening alloys will harden at room temperature, some will only harden at elevated temperatures and, in others, the process can be sped up by aging at elevated temperatures. Aging at temperatures higher than room-temperature is called "artificial aging". Although the method is similar to tempering, the term "tempering" is usually not used to describe artificial aging, because the physical processes, (i.e.: precipitation of intermetallic phases from a supersaturated alloy) the desired results, (i.e.: strengthening rather than softening), and the amount of time held at a certain temperature are very different from tempering as used in carbon-steel.