颗粒增强镁基复合材料的超声原位合成机制及组织性能研究

The particles reinforced magnesium matrix composites via in-situ method are a hot research topic in the magnesium alloys fields. In this proposal, it is solved by promoting the in-situ synthesis and dispersion of the AlN particles in the molten magnesium alloy with ultrasonic field that the problems, such as high reaction temperature, low yield and poor dispersion of particles, during the fabricating process of in-situ AlN particles reinforced magnesium matrix composites by Vapor-Liquid-Solid reaction (VLS) method. With the matrix of Mg-Al alloy and the reaction of N2, the composites are fabricated by orthogonal experiments with multi-factor, such as ultrasonic intensity, the ratio of reactants, temperature and time of reaction. The influencing factors and rules on yield, volume fraction, dispersion, morphology and particle size of AlN particles are obtained by phase analysis, microstructure observation and thermodynamic calculation. So the mechanism of in-situ synthesis and dispersion of the AlN particles in the molten magnesium alloy are explained scientifically. The macro/micro mechanical properties and mechanical behavior during plastic deformation of the composites are analyzed. Then the strengthening and toughening mechanism of the in-situ AlN particles in the magnesium matrix composites is expounded. Through this project, the theoretical foundations and technical prototypes of a novel process for fabricating the in-situ particles reinforced magnesium matrix composites will be established.

原位法制备颗粒增强镁基复合材料是目前镁材料领域的研究热点之一。本项目针对Vapor-Liquid-Solid reaction（VLS）工艺制备原位AlN颗粒增强镁基复合材料时，存在的反应温度高、产率低且颗粒分散性差等问题，提出利用超声场促进AlN颗粒的原位合成、促进其在熔体中有效分散的研究思路。以Mg-Al系镁合金为基体，以N2为反应气体，设计超声强度、反应物配比、反应温度及时间等多因素正交试验制备复合材料。通过相分析、微观组织观察等实验研究和热动力学计算等理论分析，获得原位合成AlN颗粒的产率、体积分数、分布状态、形貌、粒径等影响因素和规律，系统地阐明超声场作用下镁熔体中AlN颗粒的原位合成机制和分散机制。通过研究复合材料的宏/微观力学性能及塑性变形过程中的力学行为，阐明AlN颗粒在复合材料中的强韧化机制。通过本项目研究，为新型原位法制备颗粒增强镁基复合材料提供理论基础和技术原型。

本项目针对镁材料强度较低的不足，围绕原位AlN颗粒增强镁基复合材料展开研究。开发了超声场辅助Vapor-Liquid-Solid reaction（VLS）工艺制备原位AlN颗粒增强镁基复合材料新工艺，设计了成套的原位反应装置，获得了复合材料的制备技术原型。通过理论分析和实验研究，确定复合材料中AlN相的原位合成以Direct nitridation机制为主。阐明了温度、时间、气流量、超声功率等工艺参数对AlN颗粒产率、粒径等的影响规律，阐明了超声场对AlN颗粒的合成和分散的影响机制。研究表明，AlN颗粒的产率与温度、时间、超声功率的大小呈正比，与气流量的大小呈反比。超声场辅助下最高可将复合材料中AlN颗粒的产率提高1.5倍、粒径分布峰值减小14%。所获得复合材料的综合力学性能良好，与AZ91基体合金相比，其屈服强度、抗拉强度和延伸率可分别提高43.8%、33.6%和20.0%。通过理论分析和实验研究，基本阐明了原位AlN颗粒增强镁基复合材料中的强化机制，认为细晶强化和Orowan强化机制在复合材料中起到主要的强化作用。综上，通过本项目的研究，开发了一种高性能镁基复合材料的制备新工艺，为新型镁基复合材料的开发奠定了理论基础，为汽车、航空航天、3C等领域镁材料的开发和应用提供一种新途径。