纳米颗粒和第二相协同增强镁基复合材料的组织调控及强韧化机理

The mechanical properties of magnesium matrix nanocomposites can be significantly enhanced by the addition of nanoparticles with low content. In particular, the strengthening effect of the composites could be further improved if evenly distributed fine second phases exist in the matrix alloy. In this project the morphology, size and distribution of the second phase are controlled by the addition of TiC nanoparticles in Mg-Zn-Ca based composites after liquid forming and plastic deformation, and it is hope to reveal the effect of the nanoparticles on the second phase of TiCp/Mg-Zn-Ca magnesium matrix composites by investigating crystal orientation between the nanoparticles, the second phase and the magnesium matrix. By analyzing the evolvement rule of the TiC nanoparticles and the second phase during the regular extrusion and large plastic deformation process as well as the influence on the nucleation and growth of the dynamic recrystallization grains, the mechanical behavior and deformation mechanism of magnesium matrix composites synergistically enhanced by nanoparticles and the second phase will be illustrated. Strengthening and toughening mechanism of the magnesium matrix composite regulated by TiC nanoparticle and the second phase will be revealed. The correlative theoretical mode about evolution rule of the microstructure and mechanical properties of magnesium matrix composite enhanced by nanoparticles and the second phase under liquid forming and plastic deformation will be established. All above could provide a guidance for the design and preparation of the low-cost and high-performance magnesium-based materials.

镁基纳米复合材料具有增强体添加量少、性能提高幅度大的优势，并且基体存在细小弥散且均匀分布的第二相时，复合材料的强化效果将进一步提高。本项目拟以纳米TiC颗粒增强Mg-Zn-Ca基复合材料为研究对象，利用纳米TiC颗粒调控液态成型和塑性变形后复合材料中第二相的形态、尺寸与分布，研究纳米颗粒、第二相与镁基体之间特定的晶体学位向关系，揭示TiCp/Mg-Zn-Ca复合材料中纳米颗粒对第二相的调控机制；研究常规挤压及大塑性变形下纳米TiC颗粒与第二相的演变规律及其对基体动态再结晶晶粒形核和长大的影响规律，揭示纳米颗粒和第二相协同增强镁基复合材料的力学行为及变形微观机制，阐明纳米颗粒和第二相对镁基体的协同强韧化机理。建立液态成型和塑性变形条件对纳米颗粒和第二相增强镁基复合材料组织演变与力学性能影响规律的理论模型，为设计和制备低成本高性能镁基材料提供应用指导。

复合化是改善镁合金性能的有效途径之一，将具有尺寸效应的纳米颗粒与镁合金复合制备镁基复合材料，在轻量化需求的领域有着广泛的应用潜力和发展空间。本项目通过超声波辅助半固态搅拌铸造法制备了TiCp/Mg-4Zn-0.5Ca镁基纳米复合材料，并对其分别进行热挤压(EX)、多向锻造(MDF)和多步变形，获得了纳米颗粒和第二相协同增强镁基复合材料。随着纳米TiCp含量的增加，铸态纳米复合材料晶粒尺寸逐渐降低，晶界处块状Ca2Mg6Zn3相逐渐细化为颗粒状。当TiCp添加量为0.5wt.%时，纳米TiCp/Mg-4Zn-0.5Ca复合材料具有最优力学性能，其屈服强度(YS)、抗拉强度(UTS)和延伸率(EL)分别为75.7MPa、204.7MPa和16%。随着挤压温度、挤压速率和挤压比的降低，动态再结晶晶粒尺寸逐渐降低，MgZn2相的体积分数逐渐增加。在挤压温度190℃、挤压速率0.01mm/s和挤压比16:1时，YS、UTS和EL分别分别为355.3MPa、385.7MPa和10.2%。不同含量TiCp/Mg-4Zn-0.5Ca纳米复合材料经挤压后力学性能显著提高，随着TiCp的增加，细晶强化减弱，热错配强化增强，Orowan强化基本不变，其中由MgZn2相导致的Orowan强化减小，而由TiCp导致的Orowan强化增加。EX变形可以有效细化TiCp/Mg-4Zn-0.5Ca纳米复合材料的基体晶粒，但挤压过程中析出的MgZn2相体积分数较低；MDF同样可以实现细化晶粒组织，并促进动态析出；多步变形(MDF+EX)则结合两种变形的优势，有利于获得细晶组织的同时析出更高含量的MgZn2相。3MDF310+ED纳米复合材料具有最优力学性能，其YS、UTS和EL分别为404MPa、450.3MPa和5.2%。本项目的研究结果将为设计和制备无稀土高强韧镁基复合材料提供应用指导。