近界面组织调控对SiC颗粒增强7000系铝基复合材料强度和塑性的影响机制

SiC reinforced aluminum matrix composites (SiCp/Al) exhibit improved specific strength, specific stiffness and therefore are applied in the lightweight equipments. However, the strength of the traditional SiCp/Al composites (the matrix was 2000 and 6000 series Al alloy) is not high enough, which is only the 65-80% of the high strength 7000 series Al alloys (such as 7050). Therefore, the traditional SiCp/Al composites were not suitable to the applications with high loading. When 7000 series Al alloys are used as the matrix, the SiC particles have no contribution to the strength of the composites, meanwhile, the composites exhibit low ductility, which limit the development of high-strength aluminum based composites and their engnieering applications. In this study, we propose a new method of designing the microstructure of the region near the interface between SiC and Al matrix in 15%SiCp/7085Al. A ZnO layer will be produced on the surface of the SiC particles using Sol-Gel method. During the manufacture process of the composites, the ZnO layer will react with Al matrix to form nano MgAl2O4 particles in the region near the interface between SiC and Al matrix. The precipitation behavior of the region near the interface will be changed due to the variation of the Zn and Mg content in this region. The composites will be treated by friction stir processing (FSP), producing the mixing structure with nano grains and coarse grains or ultrafine grains and coarse grains in the region near the interface between SiC and Al matrix due to effect of the SiC particles and nano MgAl2O4 particles. The effect of nano MgAl2O4 particles on the dislocations distributed in the region near the interface will be investigated. Meanwhile, the effect of the distribution of grain size on the strength and ductility of the region near the interface will be examined. The key factors which determine the strength and ductility of the composites will be elucidated. These studies will provide references for the microstructure controlling and the application of the SiCp/7000Al composites.

SiC颗粒增强铝基复合材料（SiCp/Al）因高比强度、比刚度等特点在轻量化方面应用广泛。但传统SiCp/Al（基体为2系和6系合金）强度较低，仅为7系铝合金的65-80%，不能满足大载荷工况需求。当基体为7系铝合金时，SiC颗粒增强效果差、材料塑性低，制约了高性能复合材料的发展及其工程应用。本项目以15%SiCp/7085Al为研究对象，提出一种复合材料近界面区域微观组织设计新方法。采用溶胶凝胶法在SiC表面涂覆ZnO涂层，利用原位反应在复合材料近界面区域形成纳米MgAl2O4颗粒并改变析出相的析出行为。通过搅拌摩擦加工，利用纳米MgAl2O4颗粒在近界面区域形成超细晶和粗晶混合组织。分析纳米MgAl2O4颗粒和析出相的变化对近界面区域位错容纳能力以及晶粒尺寸分布对近界面区域强度和塑性的影响，阐明影响复合材料强度和塑性关键因素，为实现SiCp/7000Al复合材料工业化应用提供参考。

针对SiC颗粒增强7000系铝基复合材料颗粒增强效果差，材料塑性低的问题，提出复合材料近界面区域微观组织调控思路，解决材料强塑性问题。重点开展界面反应对复合材料近界面组织的影响规律，基体合金成分调控对材料界面区域析出行为的影响规律，颗粒表面改性和近界面区域晶粒调控对复合材料强度和塑性的影响规律等研究。发现界面反应引起的Mg元素偏聚是SiC颗粒增强7000系铝基复合材料强度降低的根本原因。通过调整基体合金中Zn/Mg含量比和Cu含量，改变基体析出行为，并获得了优化的合金成分使复合材料获得最佳的强塑性匹配。采用溶胶凝胶法对SiC颗粒表面改性，分别在复合材料界面区域引入纳米颗粒和碳纳米管，发现纳米颗粒降低界面区域结合强度，导致材料强塑性降低，但碳纳米管可有效提高复合材料的抗拉强度和屈服强度。制备的微米/纳米晶双尺度结构复合材料，既能发挥纳米晶的晶界强化作用，又能减少氧化物的引入，具有比单纯纳米晶结构和微米晶结构复合材料更高的强度，塑性也明显优于纳米晶结构复合材料。通过本项目的研究，阐明了影响SiC颗粒增强7000系铝基复合材料强塑性的关键因素，为复合材料体系设计、工程化制备和应用等关键技术的突破奠定了理论基础。