Microstructure of long period stacking ordered phase in an as-cast Mg-Ni-Zn-Dy alloy

An as-cast Mg-5Ni-4Zn-1Dy (wt.%) alloy was prepared by traditional ingot metallurgy. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) were used to study the microstructural characteristics of 14H LPSO phase in the as-cast Mg-5Ni-4Zn-1Dy (wt.%) alloy. Selected-area electron diffraction, convergent-beam electron diffraction, energy dispersive spectrum and high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) and atomic-resolution energy dispersive spectrum (EDS) mapping were used to study the microscopic characteristics of the 14H LPSO phase. The unit cell of 14H LPSO phase has two ABCA-type building blocks and the Zn, Ni and Dy elements were enriched on the ABCA-type stacking sequence, especially on the B and C layers. Space group of the 14H LPSO phase was determined to be P6(3)mc and atomic structural model was constructed.