A two-step dynamic recrystallization induced by LPSO phases and its impact on mechanical property of severe plastic deformation processed Mg97Y2Zn1 alloy

To explore the refinement mechanism of long period stacking ordered (LPSO) phases and its impact on mechanical properties, a typical Mg97Y2Zn1 alloy with α-Mg/LPSO binary microstructure prepared by multi-pass ECAP was systematically investigated. The obtained results indicate that during severe deformation the network 18R phase undergoes a three-step refining process, which includes kinking, zigzagging, and breaking. Lamellar 14H is precipitated first during early ECAP, and then is refined during further ECAP following a similar refining sequence of 18R phase. Moreover, a two-step dynamic recrystallization (DRX) is activated during deformation. In early passes of ECAP, DRX is promoted by 18R kinking through particle-stimulated nucleation (PSN) mechanism, and the precipitation of 14H lamellas suppresses DRX process in this period. After 14H lamellas became kinked, zigzagged and broken with more ECAP passes, the refined 14H accelerates the second step DRX process through PSN mechanism. In addition, owing to the significantly refined microstructures, both the strength and ductility of ECAP alloys increase. The ductility of ECAP alloy is improved remarkably with increasing ECAP passes. However, the increasing range of strength declines with further passes of ECAP, as the size of 18R stripes decreases gradually in the bimodal microstructures.