Dual-scale LPSO phase regulation simultaneously enhances strength and ductility of the extruded Mg-Gd-Y-Zn alloys with multimodal microstructure

Long-period stacking ordered (LPSO) phases play a central role in tailoring the mechanical response of Mg–RE–Zn alloys; however, achieving simultaneous improvements in strength and ductility remains challenging due to the complex interactions between LPSO morphology, dynamic recrystallization (DRX), and deformation modes. In this study, the micron-scale blocky LPSO phase and the nano-scale lamellar LPSO precipitate were sequentially regulated by varying the Zn content from 0 to 2.0 at.% and applying pre-aging treatments at 723 K for 0–6 h. The influence of dual-scale LPSO on the microstructure and mechanical properties of extruded alloys was systematically investigated. The study revealed that as the volume fraction of the blocky LPSO phase increases, the alloy strength continues to increase while the ductility first increases and then decreases. An optimal balance of strength and ductility is attained at a blocky LPSO fraction of 24.4% (RE/Zn = 2:1). Following pre-ageing treatment, the extruded Mg-2.0Gd-1.0Y-1.5 Zn alloy with lamellar LPSO precipitates achieved simultaneous enhancement of strength and ductility, with TYS, UTS and EL reaching 315.5 MPa, 424.9 MPa and 13.8%, respectively. The research results reveal that the blocky LPSO phase can not only refine the grains through the particle stimulated nucleation effect and grain boundary pinning, but also induces the formation of a multimodal microstructure comprising fine dynamically recrystallized grains, worked grains, and elongated LPSO phases due to the inhomogeneous plastic deformation caused by its spatial distribution. The DRX mechanism dominated by the lamellar LPSO precipitate refines worked grains while enhancing their dispersion. It also strengthens the basal texture by impeding non-basal slip. Multimodal microstructures based on blocky LPSO phases regulation achieve strength-ductility balance through texture strengthening, dislocation strengthening and short fiber strengthening. Furthermore, the incorporation of lamellar LPSO precipitates within worked grains enables synergistic enhancement of strength and ductility through enhanced strain hardening capacity.