Effects of L12 precipitates containing Zr, Er, and Y on the precipitation of Al-Zn-Mg alloys at elevated temperatures

Microalloying significantly enhances the high-temperature properties of nano-precipitates through solute partitioning at elevated temperatures. In this study, we investigated the effects of L1(2) crystal structural precipitates containing Zr, Er, and Y influence the precipitation of Al-Zn-Mg alloys using transmission electron microscopy and atom-probe tomography. The results demonstrate that the multi-addition of Zr, Er, and Y improves both ambient and high-temperature hardness of Al-Zn-Mg alloys by increasing the number density of precipitates and preventing coarsening of L1(2)/eta-MgZn2 type nano-precipitates during over-aging period at elevated temperatures. Particularly, Y forms a thermally stable L1(2) precipitate through multiple additions with Zr and Er, a finding supported by atom-probe tomography, which reveals a synergistic interaction between Er and Y. The Er and Y multi-addition increases the number density of fine L1(2)-Al-3(Zr, Er, Y) precipitates, providing heterogeneous nucleation sites for eta-type nano-precipitates at the interfaces between L1(2)/eta precipitate, thereby increasing the formation of fine eta-type nano-precipitates during the over-aging period.