镁合金的细晶化处理是提高其综合力学性能的重要措施，但细晶化处理的镁合金应变硬化能力差。目前对其应变硬化行为认识不足，这给开发高强韧镁合金结构材料带来了挑战。针对这一问题，本文设计并制备了三种具有不同显微组织特征的镁及镁合金，系统研究了晶粒尺寸、析出相及织构对镁合金应变硬化行为的影响规律，通过显微组织分析(SEM，EBSD，XRD，TEM)，揭示其应变硬化机制，为调控镁合金的组织及力学性能提供理论指导。(1)利用挤压与退火处理制备了7种晶粒尺寸的纯Mg，通过拉伸与压缩实验，系统研究了晶粒尺寸对纯Mg力学性能及应变硬化行为的影响。结果表明，晶粒尺寸小于1.5μm时，出现反Hall-Petch现象，细晶强化作用失效。应变硬化行为研究发现，纯Mg的应变硬化能力随晶粒尺寸的长大而增加，晶界滑移导致应变硬化能力急剧下降。在拉伸变形中，应变硬化指数n与晶粒尺寸(d>5.6μm)之间呈类“反 Hall-Petch”关系，并证实这一关系在其它金属中具有一定普适性。其应变硬化机制以位错滑移为主，并伴随拉伸孪生；位错密度增殖速率增加导致应变硬化能力增大。在压缩变形中，晶粒尺寸小于1.5μm 时，应变硬化转变为应变软化，并表现出超塑性。其应变硬化机制的转变归因于室温下激活了动态再结晶和晶界滑移，并伴随着少量拉伸孪生协调变形，其中晶界滑移由晶粒旋转和非基面滑移共同协调。压缩变形中，增大拉伸孪晶的增殖速率能够提高应变硬化能力。(2)采用球磨、粉末冶金结合挤压变形工艺制备了超细晶AZ61(d<1μm)镁合金，探讨了析出相对超细晶镁合金力学性能和应变硬化行为的影响。结果表明，其拉伸及压缩屈服强度均超过400MPa，消除了拉压屈服不对称性。沿晶界分布的Mg17Al12析出相能够抑制晶界滑移，避免细晶强化作用失效，从而提高屈服强度；同时消除晶界滑移对应变硬化的不利影响，并为拉伸变形中的位错滑移和压缩变形中的孪生增殖提供有利条件，使得超细晶AZ61合金具有应变硬化能力。(3)采用放电等离子烧结制备了无织构细晶AZ91镁合金，阐明了显微组织对室温压缩性能及应变硬化行为的影响规律。结果表明，细晶强化及位错强化是提高屈服强度的主要的强化机制。其应变硬化机制以位错滑移为主导，并伴随少量拉伸孪生。应变硬化指数n与晶粒尺寸d也呈“反 Hall-Petch”关系。晶内分布的层片状Mg17Al12析出相会抑制位错和孪晶增殖，不利于应变硬化能力提高。与含织构且晶粒尺寸相近的纯Mg相比，织构改变了应变硬化机制。

Grain refinement is an important process to improve the comprehensive mechanical properties of magnesium (Mg). However, the strain hardening ability of fine-grained Mg alloy is poor, and its strain hardening behavior is not well understood. It leads to a challenge to the development of Mg alloys with high strength and toughness. To address this issue, this study aimed to investigate the effects of grain size, precipitation phase, and texture on the strain hardening behavior of Mg alloys by designing and preparing three types of Mg alloys with distinct microstructure characteristics. Microstructure analysis techniques, including SEM, EBSD, XRD, and TEM, were utilized to reveal the strain hardening mechanism. The findings of this study have the potential to provide theoretical guidance for optimizing the microstructures and mechanical properties of Mg alloys.(1) The pure Mg samples with seven grain sizes were prepared via extrusion and annealing treatments. The effects of grain size on the mechanical properties and strain hardening behavior of pure Mg samples were investigated by tensile and compressive experiments. The results show that the Mg exhibites an inverse Hall-Petch relationship when the grain size is less than 1.5 μm, which indicates a failure of fine-grain strengthening. Furthermore, the strain hardening capacity of the Mg samples increases with increasing grain size, but decreases sharply due to grain boundary sliding. In the tensile test, the strain hardening exponent and grain size (d > 5.6 μm) follow an inverse Hall-Petch relationship, which is generalizable to other metals. The strain hardening mechanism is dominated by dislocation slip associated with extension twinning. Thehigher dislocation density propagation rate leads to increased strain hardening capacity. In the compressive test, the strain hardening transforms into strain softening and exhibits superplasticity when grain size is below 1.5 μm. The transformation of the strain hardening mechanism is attributed to the activation of dynamic recrystallization and grain boundary sliding at room temperature, which is accompanied by a small amount of extension twin, and the grain boundary slip is coordinated by a combination of grain rotation and non-basal slip. In compressive deformation, the higher multiplication rate of extension twins can improve the strain hardening capacity. (2) The ultrafine-grained AZ61 (d < 1 μm) magnesium alloy was prepared by ball milling and powder metallurgy combined with extrusion deformation process. The influence of precipitation on the mechanical properties and strain hardening behavior of ultrafine-grained AZ61 alloy was investigated. The results indicate that the tensile and compressive yield strengths exceed 400 MPa, and the tensile-compressive yieldasymmetry is eliminated. The Mg17Al12 precipitates distributed along the grain boundary effectively suppress the grain boundary sliding, thereby preventing the failure of finegrain strengthening and improving the yield strengths. Furthermore, the adverse effect of grain boundary sliding on strain hardening is eliminated by the Mg17Al12 precipitates, which creates favorable conditions are provided for dislocation slip during tensile test and twin multiplication during compressive test, resulting the ultrafine-grained AZ61 alloy with strain hardening ability.(3) The non-texture fine-grained AZ91 alloy was prepared by spark plasma sintering, and the influence of microstructure on the room temperature compressive properties and strain hardening behavior were investigated. The results indicate that the main strengthening mechanisms are fine-grained strengthening and dislocation strengthening. The strain hardening mechanism is dominated by dislocation slip, which is accompanied by a small amount of extension twinning. Furthermore, the strain hardening exponent exhibits an inverse Hall-Petch relationship with grain size. The dislocation and twinning are suppressed by fine-grain and intragranular lamellar Mg17Al12 precipitate, which isunfavorable for improving the strain hardening ability. Moreover, the strain hardening mechanism in the non-textured AZ91 alloy differs from that of pure Mg with texture and similar grain size.