Abstract
Precipitation in Mg-Zn alloys was analyzed by means of first-principles calculations. Formation energies of symmetrically distinct hcp configurations were determined, and potential candidates for Guinier-Preston zones coherent with the matrix were identified from the convex hull. The most likely structures were ranked depending on the interface energy along the basal plane. In addition, the formation energy and vibrational entropic contributions of several phases reported experimentally ( cubic, hexagonal, , and ) were calculated. The formation energies of cubic, and hexagonal Laves phases were very close because they were formed by different arrangements of rhombohedral and hexagonal lattice units. It was concluded that precipitates were formed by a mixture of all of them. Nevertheless, the differences in the geometrical arrangements led to variations in the entropic energy contributions which determined the high-temperature stability. It was found that the hexagonal Laves phase is the most stable phase at high temperature and thus precipitates tend to transform into the ( hexagonal) precipitates with higher aging temperature or longer aging times. Finally, the equilibrium phase () was found to be a long-range order that precipitates the last one on account of the kinetic processes necessary to trigger the transformation from a short-range order phase to .
2 More- Received 18 June 2020
- Revised 29 August 2020
- Accepted 3 September 2020
DOI:https://doi.org/10.1103/PhysRevMaterials.4.093609
©2020 American Physical Society