New poly-types of LPSO structures in a non-equilibrium Mg₉₇Zn₁Y_1.6Ca_0.4 alloy

In this study, a comprehensive analysis of microstructural features, morphology, crystal structures, and interface structures of long-period stacking ordered (LPSO) structures in a non-equilibrium Mg₉₇Zn₁Y_1.6Ca_0.4 alloy cast in a steel mold was carried out. The addition of Ca element plays an important role in the refinement of LPSO structure. The result reveals new poly-types including 20H F2F2F4, 60R \((\mathrm{F}2\mathrm{F}3\bar{\mathrm{F}}3)_{3}\) $$(\mathrm{F}2\mathrm{F}3\overline{\mathrm{F}}3{)}_3$$ , and 66H \(\mathrm{F}2\mathrm{F}3\bar{\mathrm{F}}\) $$\mathrm{F}2\mathrm{F}3\overline{\mathrm{F}}$$ 3F2(F6)₄ featuring a 6-Mg structure, alongside the prevalent 18R and 14H LPSO structures. The incoherent interface between 20H and the Mg matrix is split into two dislocation arrays, leading to the formation of a segment of 60R₁. Moreover, the superstructure 116L, designated as (F2)₁₈F4, is formed through the ordered distribution of F4 stacking faults in 18R.