Analysis of age hardening precipitates of Al-Zn-Mg-Cu alloys in a wide range of quenching rates using small angle X-ray scattering

The volume fraction of age hardening precipitates upon peak ageing after different quenching rates has been studied for five Al-Zn-Mg-Cu alloys using small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The rate of change in volume fraction of the eta' age hardening precipitates as a function of cooling rate was used to evaluate changes in the degree of solute supersaturation, and hence the quench sensitivity of the Al-Zn-Mg-Cu alloys. The results demonstrate that the amount of eta', age hardening precipitates can be changed by varying the thermomechanical processing history or the alloy compositions. It was found that the volume fraction of age hardening eta' precipitates in Al-Zn-Mg-Cu alloys increases with increasing cooling rates and increasing Mg content as well as that the size of eta' precipitates is related to the Cu/Mg ratio.