The role of melt cooling rate on the interface between 18R and Mg matrix in Mg97Zn1Y2 alloys

Abstract

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 (011¯0) 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.

Keywords

• Magnesium alloys
• Long-period stacking ordered phases
• Dislocations
• Interface structure