Aging

A change in the properties of certain metal and alloys that occurs at ambient or moderately elevated temperatures after hot working or a heat treatment (quench again in ferrous alloys, natural or artificial aging in ferrous and nonferrous alloys) or after a cold working operation (strain aging). The change in properties is often, but not always, due to a phase change (precipitation), but never involves a change in chemical composition of the metal or alloy. Related names; age hardening, artificial aging, interrupted aging, natural aging, precipitation hardening, precipitation heat treatment, progressive aging, quench aging, step aging.