Heat-treatable aluminum alloys are those that have been specifically designed to be heat treated. The term “heat treatment” refers to a process that is used to change the mechanical and/or physical properties of the alloy. There are several different types of heat treatment, and each one alters the alloy in a different way.

The application of the term heat treatable to aluminum alloys, both wrought and cast, is restricted to the specific operations employed to increase strength and hardness by precipitation hardening thus the term heat treatable serves to distinguish the heat treatable alloys from those alloys in which no significant strength improvement can be achieved by heating and cooling.

The 2xxx, 6xxx, and 7xxx series wrought aluminum alloys are heat treatable and the 4xxx series consist of both heat treatable and non-heat-treatable alloys. The 2xx.x, 3xx.x, 4xx.x, and 7xx.x series cast alloys are heat treatable. Strain hardening is not generally applied to castings.

Aluminum alloys are classified as either heat-treatable or not heat-treatable, depending on whether the alloy responds to precipitation hardening. In the heat-treatable alloy systems such as 7XXX, 6XXX, and 2XXX, the alloying elements show greater solubility at elevated temperatures than at room temperature.