Optimizing Size and Number Density of Al₃Zr Dispersoids in Al-Zn-Mg-Cu Alloys

The formation and temporal evolution of Al3Zr dispersoids in an Al-Zn-Mg-Cu alloy is investigated by in situ small-angle X-ray scattering during different homogenization treatments. The aim is to determine the most effective homogenization parameters for obtaining a high number density and small size of the dispersoids. Nucleation of the dispersoids is found to start above 400 degrees C and is boosted after isothermal holding at 425 degrees C. Regardless of the detailed homogenization profile, coarsening of the dispersoids is not observed below 450 degrees C. The results demonstrate that decreasing the heating rate, prolonging the first isothermal step, or increasing the number of steps are all beneficial regarding an increase of both, the volume fraction, and the number density of the dispersoids. Among the four investigated homogenization profiles, the one with decreasing the heating rate shows the highest impact.