How Is Aluminum Heat-Treated?

Heat-treating alters metals, usually making them stronger or more ductile.

There are four general types of heat treatments that can be applied to aluminum or its allies. They are preheating or homogenizing, annealing, solution, and precipitation heat treatment. All use massive industrial ovens, and they might require the use of chemical or water baths for cooling. The different treatments serve different purposes according to the final use of the aluminum.

Preheating

Preheating metal ingots, also called homogenizing, applies an initial thermal heat that varies greatly depending on an alloy's aluminum content. This improves the metal's workability. Products are then air-cooled for several hours. This process is usually done only to aluminum and steel alloys to be used in tool-making.

Annealing

Annealing softens strain-hardened or heat-treated aluminum alloy structures, reducing stress and stabilizing dimensions. Annealing is often done to aluminum that has been cold-worked. The metal is heated to 300 degrees and 600 degrees Fahrenheit, and it is cooled by soaking in water for up to five hours. Annealing is usually characterized by the formation of a grain structure on the aluminum, and it will be largely strain-free, with few discolorations within the grains.

Solution

Solution heat treatments involve the application of solutions to the aluminum after it is heated anywhere from 850 degrees to 1050 degrees, and they affect the alloying constituents to improve aluminum's mechanical properties. Different alloys and metal thicknesses might need to be soaked anywhere from 30 seconds to a full day. Solution heat treatments are most often used on cast, extruded or forged aluminum products.

Precipitation

Precipitation heat-treating is sometimes called artificial aging. It is sometimes conducted after solution heat-treating, and it increases tensile strength as well as ductility. Precipitation temperatures are much lower than those required for other types of heat treatments (250 degrees to 350 degrees) and often employ specialty ovens. Precipitation heat-treating is primarily used to add strength to aluminum alloys. It gets its name from the "precipitation" of atoms from alloying elements.

Clarification

Heat treatments are applied to aluminum to change the characteristics of the finished product. Heating merely to work the metal is not considered a heat treatment.

References

• Key To Metals: Heat treating of aluminum
• Metals Advisor: Heat Treating Process Description
• Wisconsin Oven Corp.: Heat Treating Definitions