Over the years, materials science has developed some innovative processes for making a variety of materials useful for any industry. With the advancement of metal-working technology following the industrial revolution, everyone from engineers to hobbyist blacksmiths have looked for creative ways to treat their metals and increase their utility.

What is age hardening?

Simply put, age hardening is the process of increasing the strength and hardness of a material by allowing particles to form precipitates out of solid solution. The process also goes by another rather intuitive name; precipitation hardening. The process was discovered by German metallurgist Alfred Wilm in 1901 while working on military research in Neubabelsberg. Since its development age hardening has become a landmark process in metallurgy.

How does it work?

Age hardening is a heat treatment that begins with a solution treatment. This involves heating a material to a high enough temperature to dissolve all solid precipitates into solution with the material matrix, then quenching to room temperature. For steels, this involves dissolving carbides into austenite, while for titanium the matrix could be alpha or beta titanium.

After the quench, the material is then brought to a lower temperature, typically 900 °F-1300 °F, and left to soak for extended times. This combination of low temperature and long soak allows those particles to precipitate out of the matrix into coherent or incoherent precipitates. These serve to impede dislocation motion within the material and thus produce a harder part.

Uses

Age hardening is typically used to increase the tensile and yield properties for some alloys of the following metals: aluminum, titanium, nickel, and stainless steel. A variety of industries use age hardening steels such as 17-4PH or 455 including the medical, aerospace, and automotive industries.

While many strengthening methods exist for steels such as strain hardening, solid solution strengthening, and traditional quench and temper, age hardening remains a valuable tool for metallurgists around the world.