幅/频/相联合调制非稳态电磁搅拌下液相金属流动的时空演化行为及其对凝固过程的影响

It is a widely applied technology by imposing varies kinds of magnetic fields during liquid metal solidification process in order to promote liquid convection and control its solidified structure. How about the mechanisms of liquid metal flow affect the solidification process and how to optimize the magnetic fields parameters and obtain a better flow state in the liquid phase in order to satisfy the solidification requirement? These are two key problems and hot points which attract continuous attention in the electromagnetic process of material field...This proposal will develop a new kind of magnetic field, which named tailored magnetic and characterized by combination modulation of amplitudes, frequencies and phases angle of a multi-phase alternating magnetic field. Following profound research are expected to be completed: (1) A power generator whose amplitudes, frequencies and phases angle can be modulated separately or combined will be designed and fabricated. (2) The spatial and temporal dynamic behavior of liquid metal fluid flow under this kind of tailored magnetic field will be measured by a specially designed physical modeling system applying low melting point liquid metal by ultra-sonic Doppler velocity meter. (3) As a simulator of solidification process in continuous casting technology, a specially designed physical modeling system will be developed in order to examine the effects of this so called tailored magnetic field on solidification quality characterized by columnar to equiaxed transition (CET), segregation and so on. (5) A totally coupled multi-physics mathematic model including magnetic fields, flow field and solidification will be established and solved. The mathematic model will be validated by comparing with the experimental results...The research of this proposal will shed light on some key problem on the relationship between flow field and solidification process. From scientific point of view, a general picture about the mechanisms of liquid phase flow affect the solidification process will form. On the other hand, from the technological point of view, a new way for control the continuous casting solidification process by applying the tailored magnetic field will develop in order to improve the solidification quality.

在金属材料凝固过程中，采用电磁场驱动液相金属流动，进而对凝固过程进行控制，有着非常广泛的应用。但液相流动对凝固过程的影响机制何在？如何根据凝固过程的特定要求，通过磁场的参数定制来设计并实现精准可控的液相流动？这两个十分关键且相互关联的基本科学问题，是学术界持续关注的热点。本项目基于磁流体力学原理，提出采用幅/频/相联合调制为特征的非稳态电磁搅拌作为金属液驱动手段，基于超声多普勒测速仪实验测量并重构表征流场，结合电磁场-流场-温度场多场耦合数值模拟和理论分析，系统研究在幅/频/相各参数单独或联合调制情况下，液态金属流动的时空演化行为，厘清液相金属流动演化规律，通过精心设计的磁场来“精准控制“凝固金属中液相流动，并达到优化控制凝固的目的；在此基础上，主要以连铸电磁搅拌为技术原型，从均匀凝固坯壳生长、促进等轴晶形成、抑制宏观偏析等角度出发，给出优化的电磁搅拌参数和技术原型。

本项目围绕连铸过程中磁场对液态金属流动以及液态金属流动对凝固过程的影响，展开了深入系统地研究。实验研究方面：建立了电磁场下连铸物理模拟实验平台，采用超声多普勒测速仪测量并重构了电磁场作用下结晶器内的二维流场，为数值模拟提供了验证支撑。数值模拟方面：（1）发展了一套结晶器电磁控流的参数优化体系，系统考察了电磁搅拌作用下结晶器内流场变化，以及钢液流动对多方面铸坯质量问题的综合影响，确定了特定坯型宽度与拉速条件下有望实现结晶器内最佳流场的优化搅拌电流，并在国内多个钢厂上线验证，极大地提升了铸坯的表面质量；（2）基于对前期电磁搅拌的认识，为了降低电磁搅拌带来负面影响，创新性地提出了复合型板坯连铸电磁控流技术（上部：电磁搅拌，下部：电磁制动）的概念，该技术综合了上述两种电磁控流技术的优点，极大地降低了电磁搅拌下的卷渣行为及提高了夹杂物的去除效率；（3）基于CAFÉ模型，建立电磁搅拌与铸坯凝固组织的关系，分析搅拌强度对等轴晶率，晶粒尺寸，的关系；（4）在带钢热镀锌领域，利用行波磁场驱动锌锅面渣运动，提高了驱渣效率。