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Precipitate crystal structure determination in melt spun Mg-1.5wt%Ca-6wt%Zn alloy
Paula M Jardim1, Guillermo Solórzano, John B Vander Sande
1Department of Materials Science and Metallurgy, Pontifícia Universidade Católica do Rio de Janeiro, C.P. 38008-Gávea, 22452 Rio de Janeiro, RJ, Brazil. paula_jardim@hotmail.com
Abstract:
A melt-spun Mg-1.5%wtCa-6wt%Zn alloy was analyzed by means of transmission electron microscopy, energy dispersive X-ray spectroscopy, and scanning transmission electron microscopy. The as-solidified alloy exhibited both spherical matrix precipitates and elongated precipitates at the grain boundaries (grain-boundary films). After heat treatment, the alloy showed faceted precipitates (cuboidal shape), mostly on dislocations. It was found that the observed precipitates are the same compound, Ca2Mg6Zn3. As there was no crystallographic data for this compound in the literature, its crystal structure was investigated by comparison of experimental and simulated selected-area electron-diffraction patterns and high-resolution electron microscopy images. This study indicated that Ca2Mg6Zn3 is a trigonal compound with space group P 3 1c and lattice parameters a = 0.97 nm, c = 1.0 nm.