The fine-grained structure in magnesium alloy containing long-period stacking order phase

Microstructural characteristics of warm-extruded magnesium alloy (Mg ₉₇Zn₁Y₂) containing long-period stacking order (LPSO) phase has been investigated using SEM and TEM as the first step to understand the effect of warm-extrusion on its mechanical property. Particular attention has been paid on the microstructural change in the hep matrix caused by warm extrusion. The microstructure developed by the warm extrusion at 623 K consists of elongated grains with fine-lamellae of LPSO phase and fine-grained matrix of hep phase. The grain size of the hep matrix observed on the cross section perpendicular to the extruding direction was about 1 urn, indicating that remarkable grain refinement was occurred during the extrusion since the grain size of as-cast alloy was around 0.5 mm. Those fine grains in the extruded alloy included abundant stacking faults, and HAADF-STEM observation revealed that the stacking faults were enriched by Zn and Y. In addition, grain boundaries were also enriched by those solute elements, which must contribute to stabilizing such fine- grained structure.