First-principles analysis of precipitation in Mg-Zn alloys

S. Liu, G. Esteban-Manzanares, and J. LLorca
Phys. Rev. Materials 4, 093609 – Published 29 September 2020
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Abstract

Precipitation in Mg-Zn alloys was analyzed by means of first-principles calculations. Formation energies of symmetrically distinct hcp Mg1xZnx(0<x<1) 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 (Mg4Zn7, MgZn2 cubic, MgZn2 hexagonal, Mg21Zn25, and Mg2Zn11) were calculated. The formation energies of Mg4Zn7, MgZn2 cubic, and MgZn2 hexagonal Laves phases were very close because they were formed by different arrangements of rhombohedral and hexagonal lattice units. It was concluded that β1 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 MgZn2 hexagonal Laves phase is the most stable phase at high temperature and thus β1 precipitates tend to transform into the β2 (MgZn2 hexagonal) precipitates with higher aging temperature or longer aging times. Finally, the equilibrium β phase (Mg21Zn25) 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 β2 to β.

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  • 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

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

S. Liu1, G. Esteban-Manzanares1, and J. LLorca1,2,*

  • 1IMDEA Materials Institute, C/Eric Kandel 2, Getafe 28906 – Madrid, Spain
  • 2Department of Materials Science, Polytechnic University of Madrid, E. T. S. de Ingenieros de Caminos, 28040 – Madrid, Spain

  • *Corresponding author: javier.llorca@imdea.org

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Vol. 4, Iss. 9 — September 2020

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