AlN纳米颗粒原位增强镁基复合材料制备及高强韧化理论研究

In order to meet the urgent demands for light-weight high-performance magnesium alloy materials in the fields of automobile and aerospace etc industries, and to improve the strength and plasticity of the conventional magnesium alloys and to reduce the cost of material processing, a precisely designed magnesium alloy melting system without the flux addition is adopted in this project. In terms of gas-solid-liquid reaction mechanism, uniformly distributed, stable and effective AlN nanoparticles as reinforcement phase having the clear and good compatibility interface with the matrix, are formed in Mg-based alloys by in-situ synthesizing methods. Sequentially, a new in-situ nanoparticle reinforced Mg-based composites can be prepared, which have practical engineering value, the as-cast tensile strength of above 300MPa, the as-cast elongation of about 40%, low cost and simple preparation process. On this basis, thermodynamics, kinetics and solute conditions of nanoparticles in-situ forming and uniform distribution will be proposed. By studying the effect of volume fraction, size and distribution of nanoparticles on the matrix alloy composition, grains size and microstructure morphology, the microstructure nature and the strengthening and toughening mechanism of nanoparticle reinforced Mg-based composites will be revealed and a theoretical model to predict the strengthening and toughening effect of nanoparticles will be built. The above researches will optimize the composites microstructure and control mechanical properties of the composites from two aspects of the composite preparation technology and theoretical control of the performance, which will provide the theoretical foundation and technical guidance for the preparation and development of novel Mg-based composites with high strength and high plasticity.

为满足我国汽车、航空航天等领域对轻质高性能镁合金材料的迫切需求，提高传统镁合金材料的强度和塑性，降低材料制备成本，本项目采用精确设计的镁合金无溶剂熔炼系统，以气－液－固反应机制为依据，通过原位反应方法在镁合金中生成均匀分布、稳定有效，且与基体结合良好、界面清洁的AlN纳米颗粒强化相，从而稳定获得具有工程应用价值，铸件拉伸强度高于300MPa，延伸率40％左右，且成本低廉、工艺简单的新型纳米颗粒增强镁基复合材料。在此基础上，研究纳米颗粒原位生成和均匀分布的热力学、动力学及溶质条件，通过研究纳米颗粒体积分数、尺寸和分布等对基体组成及晶粒大小、形貌的影响，揭示该复合材料高强高塑性的微观组织本质和强韧化机制，建立可预测纳米颗粒强韧化的理论模型。上述研究工作将从材料制备技术和性能理论控制两个方面，优化组织和调控材料力学性能，为新型高强高塑性纳米颗粒增强镁基复合材料的制备和发展提供理论依据和技术指导。

为满足我国汽车、航空航天等领域对轻质高性能镁合金材料的迫切需求，提高传统镁合金材料的强度和塑性，降低材料制备成本，本项目重点研究了纳米AlN颗粒原位强化AZ91镁基复合材料制备技术和组织控制及强韧化机理和耐腐蚀性能等指标，设计并提出了获得高强高塑、低成本AlN/AZ91复合材料的制备装置及工艺。取得的标志性成果及主要创新和结论为：（1）研制出了20-50公斤复合材料制备装置，可稳定制备出高强塑性的AlN/AZ91复合材料。其铸态室温抗拉强度230-300 MPa，延伸率17-40%，均显著高于基体AZ91合金。（2）热挤压态AlN/AZ91镁基复合材料T6热处理后，室温拉伸强度和屈服强度大于400 MPa，延伸率大于10％；（3）热挤压态AlN/AZ91镁基复合材料冷轧后，拉伸强度大于400 MPa，屈服强度大于350 MPa，延伸率大于20％；（4）轧制态AlN/AZ91镁基复合材料，室温抗拉强度可达340 MPa，屈服强度大于300 MPa，延伸率大于20％，250℃下断后延伸率超过了60%；（5）200℃，50MPa应力条件下，铸态AlN/AZ91复合材料的疲劳寿命可达401h，是基体AZ91疲劳寿命的3倍，蠕变速率为2.08×10-8/s，比基体AZ91低一个数量级；（6）AlN颗粒的形成不仅没有降低铸态和T6热处理态复合材料的耐腐蚀性能，而且有一定程度提高。（7）AlN/AZ91复合材料的强化机理主要为晶界强化与第二相强化。构建了仅与原位反应时间相关的强度预测模型，可准确预测铸态AlN/AZ91 复合材料的屈服强度。（8）发现了室温下原位AlN 增强相促进锥面<c+a>可动位错形核的实验证据。分析表明AlN 增强相降低了锥面<c+a>位错形核的临界分切应力（CRSS）并有效抑制了锥面<c+a>位错的基面转变，从而能够使大量的锥面<c+a>可动位错在铸态AlN/AZ91 复合材料室温变形过程中被激活。本研究成果解决了当前镁合金及其复合材料存在强度低、塑性差的技术瓶颈，在不提高制备成本和降低耐腐蚀性能的前提条件下提高了AZ91镁合金的强度和塑性，其制备技术可推广应用于AZ19镁合金的改性和应用范围的扩展。本项目的完成可推动我国镁合金及其复合材料的发展水平，为镁合金产业的可持续发展提供技术指导和理论基础。