Compositional Transition Layer around Growing LPSO in Mg₉₇Zn₁Y₂ Cast Alloys

Abstract

Using conventional transmission electron microscopy (TEM) and aberration-corrected high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), compositional irregularity has been identified around long-period stacking order structures (LPSOs) in aged Mg 97 Zn 1 Y 2 alloys, which have coexistence of LPSO and ¡-Mg matrix. Elemental mappings show that compositional transition layers surround the growing LPSOs. The compositional transition layer includes solute atmosphere in the ¡-Mg matrix and transition layers of LPSOs with lower concentrations of solute elements. The Zn concentration in a transition layer of LPSO is higher than that of Y, which differs from the ¡-Mg matrix and LPSOs. The transition layer is an 18R-type stacking sequence. No transition layer was observed after the transformation from 18R-type to 14H-type LPSOs. These results indicate that the segregation of Zn is faster than that of Y, and that the transition layer is a nonstoichiometric 18R-type LPSO with Zn-rich lower concentration of the solute elements, which connects an 18R-type LPSO and an ¡-Mg matrix.