The influence of the quench rate on the microstructure and the ageing response of a Zr-containing Al-Zn-Mg alloy was investigated. It is shown that Al3Zr dispersoïds are efficient nuclei for precipitation of coarse, equilibrium η precipitates during the quench. Dispersoïds are heterogeneously distributed in bands, resulting in bands of quenched-induced precipitates after a slow quench. The ageing response after a slow quench is characterized by various levels of heterogeneities resulting in a 'composite' material. On a microscopic scale, quench-induced η precipitates are surrounded by a precipitate-free zone. On a mesoscopic scale, the material is separated in unperturbed regions and regions of high density of coarse precipitates and low density of hardening precipitates. Finally, a slow quench makes the material more sensitive to the heating rate to the ageing temperature, due to slower GP zone precipitation during natural ageing because of annihilation of vacancies during quenching.
|Number of pages||8|
|Journal||Materials Science and Engineering A: Structural Materials: Properties, Microstructure and Processing|
|Publication status||Published - 15 Aug 1998|
- Al-Zn-Mg alloys
- Precipitation hardening
- Precipitation kinetics