三维高强超声场中复杂偏晶合金的液相分离与组织控制研究

Although the solidification process of metallic alloys within ultrasonic field has been studied extensively, the main research method is only applying one dimensional ultrasound into the solidifying alloy melt, whose disadvantages are the rapid attenuation of sound wave and the limited effective range inside liquid phase. In this project, we intend to introduce three dimensional orthogonal coherent and non-coherent ultrasonic waves into ternary Al and Cu based monotectic alloys. The effect of ultrasound on liquid phase separation and solidification process is emphasized. Firstly, the 3D ultrasonic wave propagation features within liquid alloy is studied in order to clarify the dynamics of cavitation effect and kinematics of acoustic streaming. Secondly, the nucleation characteristics of second liquid phase under cavitation effect are explored. The motion of second liquid droplet within 3D ultrasonic fields under the coupled influences of acoustic streaming, Stokes motion and Marangoni convection is investigated, based on which the dynamic conditions for the complete suppression of macrosegregation and the formation of uniform microstructure is elucidated. Meanwhile, the competitive nucleation mechanism among solid and liquid phases during monotectic transition is also studied. The dynamic response of monotectic microstructure and solute redistribution to the 3D ultrasonic fields is revealed in details. Finally, the relationship among “3D acoustic parameter—microstructure—physical property” is experimentally established in order to find an effective way to control microstructure and applied properties of ternary monotectic alloy.

虽然对于超声场中凝固过程已有较多研究，但通常仅用一维超声波施加到合金熔体内部，具有能量衰减快和作用范围小等局限性。本项目采用三束正交的相干和非相干超声波建立三维动态凝固条件，研究三元Al/Cu基复杂偏晶型合金的液相分离和组织形成机理。首先，分析合金熔体中三维超声波的传播规律，确定空化动力学和声流运动学特征。其次，探索超声空化对第二液相形核的作用机制，研究液相分离过程中声流效应、Stokes 运动和Marangoni 对流的耦合作用方式，明确第二相液滴的生长、运动和聚集规律, 揭示彻底抑制宏观偏析并形成均匀液相分离形态的动力学条件。同时，研究三维高强超声场中偏晶固相和液相竞争形核机制，分析组织演化和溶质截留对三维超声场的动态响应特性。最后，建立“三维超声—组织形态—物理性能”的内在联系，寻求利用三维高强超声场调控偏晶型合金凝固组织和应用性能的有效途径。

本项目采用三维高强超声技术，结合数值模拟计算，研究了三元Al基和Cu基偏晶合金在超声场中的液相分离和动态凝固过程，主要取得了以下四方面成果：一是自主设计并研制了三维超声凝固实验装置，实现了Al基和Cu基偏晶合金在一到三维超声场中的液相分离和凝固过程。二是通过数值计算，揭示了不同维度超声作用下偏晶熔体中的声场和流场分布特征，阐明了超声场中空化泡的运动学和动力学规律。计算结果表明，三维正交超声波的施加能够显著增大合金熔体内部空化效应作用范围和声流的平均速度，强化超声场对于凝固过程的作用效果。三是系统探索了超声作用下Al基和Cu基偏晶合金的液相分离和动态凝固机制。结果证实，三维超声场的施加能够抑制静态条件下偏晶合金由于液相分离引发的宏观偏析，形成具有均匀弥散结构的大体积偏晶材料。阐明了超声空化效应和声流对于偏晶液相分离过程的作用机理，提出了形成均匀弥散偏晶组织的动力学条件。四是建立了“三维超声—组织形态—物理性能”的内在联系，寻求出通过三维超声技术调控偏晶合金力学、耐磨和耐腐蚀等应用性能的有效途径。.以上述四方面研究结果为主要内容，发表SCI和EI论文共计23篇，出版学术专著1部，申请和授权国家发明专利共计11项，获陕西省科学技术二等奖1项。项目负责人翟薇教授获2019年度国家自然科学基金优秀青年科学基金项目资助。培养博士研究生3人，硕士研究生2人。本项目的研究丰富和发展了超声作用下的金属材料动态凝固理论，同时为高性能金属材料的制备提供了新颖的技术路径。