Small-angle X-ray scattering study of precipitates in AlZnMgCu-1.0 wt.% Li alloy

The precipitate size, distribution and volume fraction in an AlZnMgCu-1.0 wt.% Li alloys during various aging conditions were investigated by small-angle X-ray scattering and transmission electron microscopy. According to the selected area diffraction patterns, the prime precipitates in this alloy are η′ phases, not δ′ phases. During the temperature ranging from 120 to 160 °C, the growing of precipitates in the 7055-1.0 wt.% alloys is not apparent. From 120 to 150 °C, the varieties of precipitate volume fraction depend on the competition between dissolution rate of GP zones and nucleation rate of η′. At 160 °C, the growing of η′ precipitates is undergoing a Lifshitz-Slyozov-Wagner coarsening process, and the prime thermodynamic reaction is the nucleation growth of η′ precipitates.