Alterungshärten

Alterungshärten, also known as age hardening or precipitation hardening, is a heat treatment process used to increase the strength and hardness of certain alloys. This process is primarily applied to aluminum alloys, but can also be used for some steels and nickel alloys. The fundamental principle behind aging is the controlled formation of small, uniformly dispersed particles within the metal's microstructure. These particles impede the movement of dislocations, which are line defects in the crystal lattice that allow for plastic deformation. By restricting dislocation motion, the material becomes stronger and harder.

The aging process typically involves two main steps. The first is a solution heat treatment, where the alloy is heated to a high temperature to dissolve the alloying elements into a single solid solution. This is followed by a rapid quench to a lower temperature, which traps these elements in a supersaturated solid solution. The second step is the aging treatment itself, which can be done at room temperature (natural aging) or at an elevated temperature (artificial aging). During aging, the supersaturated solid solution becomes unstable, and the dissolved elements begin to precipitate out as finely dispersed particles. The size, distribution, and coherency of these precipitates are critical for achieving the desired mechanical properties. Over-aging occurs when the precipitates grow too large or become less coherent, leading to a decrease in strength. Therefore, the aging time and temperature must be carefully controlled to optimize the hardening effect.