LAUSR

Abstract In aged Mg–Y–Ce alloys, the morphology and composition of the β ' metastable precipitates were investigated by high-angle annular dark-field scanning transmission electron microscopy (HAADF−STEM). The addition of Y and Ce into α-Mg matrix lead to the formation of the β L ' and β S ' precipitates with a different orthorhombic lattice parameter b. It is found that there are obvious differences in morphology and composition between the β L ' and β S ' precipitates. Compared to the β L ' precipitate with an elliptical shape, the β S ' precipitate has a smaller lenticular shape, which is caused by a significant strain between the β S ' and α-Mg matrix phases along a 11 2 ¯ 0 α direction. More notably, Y and Mg atoms make up the relatively stable β L ' precipitate, whereas, Ce is found to preferentially facilitate the formation of the β S ' precipitate, which is unstable and evolved into the β 1 precipitate easily.