纳米SiCp/AZ91镁基复合材料中第二相析出行为及高温变形机制研究

The aim of this project is to investigate the precipitation behavior of secondary phase and elevated temperature deformation behavior of magnesium matrix nanocomposites reinforced with SiC nanoparticles. By optimizing stir casting assisted ultrasonic vibration technology, it is hoped to obtain the SiCp/AZ91 nanocomposites with uniform nanoparticle distribution. By analyzing the microstructure of nanocomposites subjected to multidirectional forging (MDF) under constant temperature, it is hope to illustrate the effect of SiC nanoparticles on the nucleation site, size and distribution of secondary phase. And the coordinate effect of SiC nanoparticles and secondary phase on the DRX nucleation and grain growth is to be revealed by researching the microstructure evolution of the nanocomposite and analyzing the interface structure evolution of the secondary phase during MDF under decreasing temperature. By researching the microstructure and properties of fine-grained magnesium matrix nanocomposites after elevated temperature compression, it is hoped to reveal the influence of SiC nanoparticles and secondary phase on the high temperature deformation behavior of the nanocomposites. The room temperature deformation mechanism and fracture mechanism of the nanocomposite will be researched. The strengthening effect of SiC nanoparticles and secondary phase is to be revealed. By investigating the effect of SiC nanoparticles on secondary phase and revealing its control factor, this project will have important theoretical value on the development of magnesium matrix composites reinforced with nanoparticles.

本课题拟就纳米SiCp/AZ91镁基复合材料中第二相的析出行为及高温变形机制进行研究。通过搅拌铸造复合超声波分散法，制备纳米颗粒分布均匀的纳米SiCp/AZ91镁基复合材料。研究恒温多向锻造后纳米SiCp/AZ91复合材料的显微组织，揭示纳米SiCp对第二相析出、尺寸、分布的影响规律。阐明降温多向锻造过程中纳米复合材料中第二相的演变机理和相界面结构演化规律，揭示纳米SiCp同第二相的协同作用对DRX形核及晶粒长大的影响机制。研究细晶镁基纳米复合材料高温压缩后的微观结构和性能，揭示纳米SiCp和第二相对细晶镁基纳米复合材料的高温变形行为的影响机制。研究纳米SiCp增强镁基复合材料的室温变形机制及断裂机理，揭示纳米SiCp与第二相对基体合金的强化机制。本课题通过研究纳米SiCp对第二相的影响规律，揭示纳米复合材料中第二相的控制因素，对纳米颗粒增强镁基复合材料的开发具有重要的理论指导意义。

镁基纳米复合材料结合了镁合金与纳米尺度增强体的优势，具有满足特殊性能需求的潜在应用背景。通过加入纳米陶瓷颗粒，镁基体的性能有望得到显著提升。本项目通过复合半固态搅拌铸造与超声波处理制备了铸态纳米SiCp/AZ91镁基复合材料，并对铸态纳米SiCp/AZ91镁基复合材料进行不同条件下的多向锻造，获得了细晶镁基纳米复合材料。纳米颗粒对晶界的钉扎作用显著细化了镁基体晶粒。与铸态复合材料相比，恒温条件下6道次锻造后纳米SiCp/AZ91复合材料的屈服强度、抗拉强度和伸长率同时提高。相同多向锻造条件下，与AZ91合金相比，纳米颗粒的加入进一步提高了镁基体的屈服强度。随着锻造温度的降低和道次的增加，镁基体中的析出相数量逐渐增加，这些析出相也具有阻碍晶粒长大的作用。而降温条件下多向锻造后纳米复合材料中由SiC纳米颗粒聚集和第二相构成的纳米颗粒带加速了室温拉伸变形中裂纹的扩展。系统研究表明纳米SiCp/AZ91复合材料的力学性能取决于晶粒尺寸、第二相和颗粒分布等。随着热压缩温度升高和变形速率的降低，细晶纳米复合材料中的变形带逐渐消失，晶粒逐步细化。与铸态纳米复合材料相比，峰值应力后细晶纳米复合材料的动态软化阶段无显著差异。细晶纳米SiCp/AZ91复合材料的激活能低于铸态纳米复合材料，但其可加工区显著增加，并且可加工温度较铸态复合材料降低。本项目的研究结果将为设计和制备低成本高性能镁基材料提供应用指导。