为明确含长周期堆垛有序(LPSO)相Mg‑Zn‑Y系合金在高应变速率剪切条件下的强度响应、主导变形机制及其与显微组织演化的耦合关系，本工作采用分离式Hopkinson压杆(SHPB)装置，在800~1800 s^-1应变速率下，对铸态和挤压态合金的组织演化和动态力学行为进行了对比分析。结果表明，随着应变速率由800 s^-1提升至1800 s^-1，挤压态Mg-4Zn-12Y合金的极限抗压强度由279.16 MPa提升至354.78 MPa，增幅约为27.1%。加入Sn元素后，随着应变速率由800 s^-1提升至1600 s^-1，挤压态合金的极限抗压强度由342 MPa提高至433 MPa，提升幅度约为26.6%。Sn元素的加入增强了合金的强度和加工硬化能力。其中，{1012}拉伸孪晶是协调塑性应变的主要方式，LPSO相的扭曲在协调变形中起到了关键作用。同时，在晶界三叉结处观察到大量几何必需位错的聚集，该现象导致局部晶格发生显著畸变，并为孪晶形核提供了有利条件。此外，LPSO相周围发生了动态再结晶，其主要由颗粒诱发形核机制及LPSO相与基体界面的复杂形貌所驱动。

Lightweight Mg alloys are desirable for transportation and defense applications owing to their high specific strength and energy‑absorption capacity under impact loading. Among these, Mg–Zn–Y alloys containing long-period stacking-ordered (LPSO) phases exhibit exceptional comprehensive mechanical properties; however, their deformation behavior and underlying micromechanisms under high-speed shear remain poorly understood. Therefore, this study performs a comparative analysis of the microstructural evolution and dynamic mechanical behavior of as-cast and extruded Mg–Zn–Y–0.3Sn (mass fraction, %) alloys containing LPSO phases using a split Hopkinson pressure bar at strain rates ranging from 800 s⁻¹ to 1800 s⁻¹. The aim is to elucidate the strength response, identify the dominant deformation mechanisms, and clarify how microstructural evolution, including features characteristic of LPSO-containing Mg–Zn–Y alloys, couples with the high-strain-rate shear response. The results show that as the strain rate increases from 800 s⁻¹ to 1800 s⁻¹, the ultimate compressive strength of the extruded Mg–4Zn–12Y alloy increases from 279.16 MPa to 354.78 MPa, showcasing an enhancement of approximately 27.1%. Similarly, increasing the strain rate from 800 s⁻¹ to 1600 s⁻¹ raises the ultimate compressive strength of the extruded Mg–4Zn–12Y–0.3Sn alloy from 342 MPa to 433 MPa, corresponding to an improvement of approximately 26.6%. The Sn addition enhances the alloy’s strength and work-hardening capacity. The {1012} tensile twinning primarily serves to coordinate plastic strain, whereas kinking the LPSO phase plays a critical role in coordinating the deformation. High densities of geometrically necessary dislocations accumulate at grain-boundary triple junctions, producing considerable local lattice distortion and providing favorable conditions for twin nucleation. Furthermore, dynamic recrystallization occurs around the LPSO phase, driven primarily by the particle-stimulated nucleation mechanism and the complex morphology of the LPSO phase/matrix interface. These findings provide crucial insights into the deformation micromechanisms of LPSO-containing Mg alloys under high-strain-rate conditions.