The role of melt cooling rate on the interface morphology and dislocation configuration between 18R long-period stacking ordered (LPSO) structure and Mg matrix in Mg₉₇Zn₁Y₂ (at.%) alloys was investigated by atomic-scale HAADF-STEM imaging. The 18R/Mg interface is step-like both in the near-equilibrium alloy and non-equilibrium alloy. Lower cooling rate makes the step size more regular and larger. Only 54R structure can be observed at the interface in the near-equilibrium alloy, and the dislocations are highly ordered. 54R and 54R′ structure sandwiched by b₁ and b₂ + b₃ dislocation arrays, and new dislocation configuration can be detected at the interface in the non-equilibrium alloy, but the dislocations are less ordered. 18R/Mg interface containing 54R or 54R′ in equilibrium width, parallel to the (01-10）plane, should be most stable based on elastic calculation. The segregation of solute atoms and its strong interaction with dislocations dominate the LPSO/Mg interface via diffusion-displacive transformation.

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