Microstructure evolution of Al-Zn-Mg-Cu alloy during non-linear cooling process
(1. School of Materials Science and Engineering, Central South University, Changsha 410083, China;
2. Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education,
Central South University, Changsha 410083, China;
3. Nonferrous Metal Oriented Advanced Structural Materials and Manufacturing Cooperative Innovation Center,
Central South University, Changsha 410083, China)
2. Key Laboratory of Nonferrous Metal Materials Science and Engineering, Ministry of Education,
Central South University, Changsha 410083, China;
3. Nonferrous Metal Oriented Advanced Structural Materials and Manufacturing Cooperative Innovation Center,
Central South University, Changsha 410083, China)
Abstract: The microstructure evolution and properties of an Al-Zn-Mg-Cu alloy were investigated under different non-linear cooling processes from the solution temperature, combined with in-situ electrical resistivity measurements, selected area diffraction patterns (SADPs), transmission electron microscopy (TEM), and tensile tests. The relative resistivity was calculated to characterize the phase transformation of the experimental alloy during different cooling processes. The results show that at high temperatures, the microstructure evolutions change from the directional diffusion of Zn and Mg atoms to the precipitation of S phase, depending on the cooling rate. At medium temperatures, η phase nucleates on Al3Zr dispersoids and grain boundaries under fast cooling conditions, while S phase precipitates under the slow cooling conditions. The strength and ductility of the aged alloy suffer a significant deterioration due to the heterogeneous precipitation in medium temperature range. At low temperatures, homogeneously nucleated GP zone, η′ and η phases precipitate.
Key words: Al-Zn-Mg-Cu alloy; microstructure evolution; non-linear cooling; electrical resistivity; mechanical property