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 P31c and lattice
parameters a = 0.97 nm, c = 1.0 nm.