Inherited multimodal microstructure evolution of high-fracture-toughness Mg-Zn-Y-Al alloys during extrusion for the consolidation of rapidly solidified ribbons

Abstract

The mechanisms of multimodal microstructure evolution and the effects of microstructural factors on mechanical properties must be elucidated to design new alloys with superior properties. In this study, high-fracture-toughness and ductile Mg96.75Zn0.85Y2.05Al0.35 alloys were developed using rapidly solidified (RS) ribbon-consolidation technique, and the inherited multimodal microstructure evolution during plastic flow consolidation of the RS ribbons was investigated. The use of extrusion for plastic flow consolidation of the heat-treated RS ribbons produced a multimodal microstructure consisting of the worked grains with high Kernel average misorientation (KAM) angles (Group 1), the ultrafine dynamically recrystallized (DRXed) grains with intermediate KAM angles (Group 2), and the fine DRXed grains with low KAM angles (Group 3). Groups 1 and 2 contribute to the alloy strengthening, while Group 3 contributes to improving ductility with strain-hardening, resulting in enhancement of the fracture toughness. To form the multimodal microstructure, it was necessary to apply plastic flow with equivalent strains of >2.3 to the heat-treated RS ribbons possessing duplex microstructures with different dispersions of the long-period stacking ordered phase.