An insight into two categories of novel Ce-rich superstructures in Mg-Ce alloys

For rare earth magnesium (Mg-RE) alloys after solution and aging treatments, some early occurred me-tastable precipitates or structures could play a crucial role in an initial rapid ascent of alloy hardness. In this study, the early precipitation products of an aged Mg- 3.0 wt%Ce alloy were investigated particularly by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). With a fully coherent relation to & alpha;-Mg matrix, two types of novel Ce-rich ordered struc-tures were identified as 6 H and 18R-type superstructures, respectively. The 6 H-type superstructure has a composition of Mg66Ce6 and a hexagonal structure (a = 1.12 nm 2 3 a and c = 1.56 nm 3c , where a and c denote lattice parameters of & alpha;-Mg matrix) with space group (No. 193). The 18R-type superstructure crystallizes in a trigonal structure (a = 1.92 nm 6a , c = 4.62 nm 9c ) with space group R 3 m (No. 166) and a composition of Mg210Ce6.& COPY; 2023 Elsevier B.V. All rights reserved.

Automated summary

In this study, the early precipitation products of an aged Mg- 3.0 wt%Ce alloy were investigated using aberration-corrected HAADF-STEM. Two novel Ce-rich ordered structures, namely 6 H and 18R-type superstructures, were identified.