Quick Age hardening is a process in which a uniform dispersion of a fine, hard coherent precipitate is produced within a sofer, more ductile matrix. Age hardeining is also known as precipitation hardening.
Schematic
Solution treatment
Quench
Age
The picture on the left is a eutectic binary phase diagram and the pictures on the right represent the microstructures throughout the process.
1. Solution Treatment
During the solution treatment, the alloy is first heated above the solvus temperature and held until a homogeneous solid solution α is produced. This step dissolves the β precipitate and reduces any segregation present in the original alloy.
The alloy could be heated to just below the solidus temperature and the rate of homogenization could be increased, but the presence of a nonequilibrium eutectic microconstituent could cause melting. Therefore, the alloy is solution treated between the solvus and eutectic temperatures.
2. Quench
After solution treatment, the alloy, which contains only &alphs; in its structure, is rapidly cooled, or quenched. The atoms do not have time to diffuse to potential nucleation sites, so β does not form. After the quench, the structure still contains only α. The α is a supersaturated solid solution αss containing excess B, and it is not an equilibrium structure.
3. Age
Finally, the supersaturated α is heated below the solvus temperature. At this aging temperature, atoms diffuse only short distances. Because the supersaturated α is not stable, the extra B atoms diffuse to numerous nucleation sites and precipitates grow. Eventually, if the alloy is held for a sufficient time at the aging temperature, the equilibrium α + β structure is produced.
