由变形粗晶与再结晶细晶组成的双峰组织可兼顾高强度和高塑性。其中细晶能有效阻碍位错的运动，提供高强度；粗晶为累积的位错提供额外的容纳空间，提高塑性。本工作通过控制挤压工艺在AZ31镁合金中构筑双峰组织，研究了双峰组织的形成机制及其变形行为。双峰组织的形成归因于塑性变形阶段的不完全动态再结晶以及第二相粒子的激发成核效应。变形过程中，细晶承受较大的应力，而粗晶则承载更多的应变。细晶是AZ31镁合金强度显著提升的关键，粗晶的协调变形作用则为其优异的塑性提供了保障。得益于双峰组织良好的变形能力，对双峰组织AZ31镁合金进一步挤压，成功制备了细晶AZ31镁合金，合金展现出优异的力学性能：抗拉强度达到265 MPa，屈服强度为112 MPa，并保持了19%的伸长率，实现了强度与塑性的协同提升。

The magnesium alloy exhibits a notable plasticity limitation due to its hcp structure. In recent years, the development of a bimodal structure, consisting of deformed coarse grains and recrystallized fine grains, has emerged as an effective strategy to balance the strength and plasticity of magnesium alloys, offering a new avenue for property. This optimization study investigates the formation mechanism and deformation behavior of the bimodal structure in AZ31 magnesium alloy by controlling the extrusion process. The formation of the bimodal structure is attributed to the incomplete dynamic recrystallization during plastic deformation and the particle-stimulated nucleation effect of the secondary phase. During deformation, fine grains endure higher stresses, while coarse grains accommodate more strain. The fine grains significantly contribute to the improved strength of the AZ31 magnesium alloy, while the coordinated deformation of the coarse grains ensures excellent plasticity. Leveraging the superior deformation capability of the bimodal structure, fine-grained AZ31 magnesium alloy was successfully fabricated through further extrusion, achieving outstanding mechanical properties: a tensile strength of 265 MPa, a yield strength of 112 MPa, and an elongation of 19%. This demonstrates the synergistic enhancement of strength and plasticity.