铝熔体中纳米SiC的超声辅助分散及压力成形均匀分布调控机制

Developing efficient material preparation methods to make nano particles easily added into molten melt, avoiding segregation in crystal boundary and uniformly dispersed in metal matrix are pressing questions in metal matrix nano-composites (MMNCs) researches. In this project, the rational combination of energy ball milling method, ultrasonic dispersion method and semi-solid rheocasting is proposed for preparing aluminum matrix nano-composites. In this processing, a nano-ceramic particles/Al composite powder is firstly prepared by high-energy ball milling method and formed as particles or billets, then molten method is applied and composite billet is added into melt, and dispersion enhanced by by ultrasonic vibration while the composite powder billets are remelted. Finally the semi-solid slurry of MMNCs is formed by rheo-squeeze casting or die-casting to obtain components with a compacted and uniform microsturcture under rapid cooling and high pressure. First, the variations of microstructure and morphology of the composite powder under high energy ball milling process will be studied. Then dispersion mechanism of the composite powder billets and its influence factors under ultrasonic vibration will be investigated. Next, microstructural evolution mechanism of composite powders and solidification behavior of the MMNCs semi-solid slurry under ultrasonic vibration will be studied. Finally, systematical research on the microstructure of rheo-squeeze casted components and its influence on the mechanical properties will be proposed. On this basis, an economic and efficient process, high-energy ball milling and ultrasonic rheocasting, which combining the preparation and forming for aluminum matrix nano-composites will be explored.

开发高效的材料制备方法，使纳米增强颗粒较容易地加入熔体中，并避免偏聚于晶界而均匀分布于基体中，是金属基纳米复合材料（MMNCs）领域亟待解决的关键问题之一。本项目针对纳米SiC增强铝基复合材料，提出将高能球磨技术、超声分散技术及半固态流变成形工艺有机结合，首先利用高能球磨工艺制备出纳米SiC颗粒/Al复合粉粒或粉坯；然后利用熔炼铸造法加入复合粉坯，通过对熔体进行高能超声处理进一步分散纳米增强颗粒；最后利用流变挤压铸造或高压铸造成形下的高压和较快的冷却速度，获得结构致密、颗粒分布均匀的零件。主要研究高能球磨过程中复合粉末的形貌、组织变化规律；研究超声作用下熔体中复合粉坯的分散机理及影响因素；研究不同压力及冷却速度下复合浆料凝固过程中纳米颗粒均匀分布的综合调控机制；系统研究流变压力铸造成形凝固组织及其对力学性能的影响规律。为开发出经济、高效的集MMNCs的制备与成形于一体的新技术提供理论基础。

本项目针对纳米颗粒难以加入铝熔体、以及难以在铝基体中均匀分布等问题，建立了纳米SiC颗粒增强铝基复合材料的液态制备新工艺。采用球磨预分散——固-液混合——机械搅拌——超声分散——铸造成形工艺，实现了纳米SiC颗粒在铝基体中的较均匀分布，制备出了较高性能的纳米SiC颗粒增强铝基复合材料。获得了纳米颗粒含量与SiCP/Al-Si复合材料组织及性能的关系，纳米SiCP含量增高时，材料的强度及韧性能够同时提高。制备出纳米SiCP/Al-5Cu复合材料，并获得了制备工艺参数与组织及性能的关系。获得了纳米SiC颗粒增强铝基复合材料熔体在不同成形压力下凝固的组织及性能变化规律，在0 400MPa压力下，随着压力的增加，纳米SiC颗粒的分布越来越均匀，基体组织的晶粒也越来越细小；复合材料的力学性能增加。获得了纳米SiC颗粒含量与复合材料熔体的表观粘度关系的规律性认识。纳米SiCP含量增高时复合浆料的表观粘度显著提高，获得了纳米SiC颗粒含量与复合材料熔体表观粘度关系的数学模型，对判断复合材料熔体的流动性及充型能力具有重要意义。设计并制备出新型纳米SiCP与Mg2Si混杂增强的（SiCP+Mg2Si）/Al-5Cu复合材料，两种增强相有相互细化及均匀分布效果，材料性能显著提高。