Metal Heat Treatment: Age Hardening
Heat treatments are one of the most important processes used in metal fabrication and metalworking. Heat treatments can increase the strength and hardness of metals, reduce the amount of formability in certain applications, increase ductility and reduce the risk of corrosion. Heat treatment can also improve fatigue strength and resistance to malleability. Heat treatment is achieved by heating the material to a specific temperature and then cooling it quickly.
Age hardening is a form of heat treatment used to increase the strength of metals. It’s also known as precipitation hardening. During age hardening, a material is heated up to above its recrystallisation temperature. This causes the crystalline structure of the material to change, where certain elements become more concentrated within the material. These concentrated elements create what’s known as precipitates, which are widely spaced structures that are dispersed throughout the material. These precipitates weaken the lattice bonds of a metal, allowing for improved strength and hardness.
The age hardening process involves heating the metal up to a temperature which is well above its recrystallisation temperature. This is known as the solution heat treatment. The heated metal must then be rapidly cooled, ideally using a quench or water jacket. During this cooling process, various elements in the metal start to arrange into interlocked clusters. This is known as a supersaturated solid solution. This causes the metal to become more ductile, allowing for improved tensile strength and fatigue strength.
The metal is then treated with a process known as Aging, or Artificial Aging. This process is undertaken by heating the metal up to a specific temperature and then leaving it to cool at room temperature. During this process, certain elements within the metal are more likely to form precipitate clusters. These clusters of elements lower the mobility of certain metals in the material, which further strengthens the material. This can help to increase the hardness of the metal and the overall strength of the material.
Age hardening is a process that can be used to greatly improve the strength of metals. It involves heating the metal up to a specific temperature, cooling it quickly and then allowing it to age at room temperature. This process causes specific elements within the metal to form precipitate clusters which make the metal stronger. It’s a relatively simple yet effective process that is used in many different types of metalworking and metal fabrication.
