多磁效应协同控制二元合金枝晶凝固过程微观偏析的机理研究

Microsegregation influences mechanical properties, corrosion resistance and workability of ingots. It is of much importance for optimizing alloy properties and casting processes to study microsegregation. Several factors such as undercooling, solid back diffusion, dendrite coarsening and solidus/liquidus temperature influence microsegregation during dendritic solidification. The steady high magnetic field as a powerful tool has been paid wide attention to in metal material processing. It was found that the magnetic field significantly changed undercooling, diffusion and melt flow during alloy solidification with aid of multi magnetic effects, variation of which without doubt changes microsegregation of solutes. In the project, we mainly employ the directional solidification, thermal analysis and diffusion couple techniques to explore the change in solid back diffusion, tip undercooling and secondary dendrite arm spacing in the magnetic field. The solute distribution, distribution coefficient and amount of non-equilibrium phases are investigated on the action of multi magnetic effects. Mechanism of microsegregation is clarified in the magnetic field and its model will be built up. The work aims to reveal the nature of microsegregation and provides a scientific theory for effectively applying the magnetic field to control microsegregation during alloy solidification and developing relevant solidification technologies.

微观偏析影响合金铸坯的力学性能，腐蚀阻抗及加工性能，研究微观偏析对优化合金性能及铸造工艺具有重要的意义。很多因素会影响枝晶凝固过程溶质的微观偏析行为，如：过冷度，固态逆扩散，枝晶粗化及固/液相线等。稳态强磁场作为一种强大的金属材料制备调控方式已经引起了人们广泛的关注。磁场通过多种磁效应明显改变金属凝固过程中的过冷度，元素扩散，熔体流动等，这些因素的变化无疑会改变溶质的微观偏析规律。本项目以定向凝固技术，热分析法及扩散偶法等为主要实验手段，探索磁场下二元合金枝晶凝固过程固态逆扩散，尖端过冷度，枝晶粗化动力学等变化规律，研究多磁效应协同作用下溶质分布，分配系数，非平衡相数量等变化规律，明确磁场对溶质微观偏析行为的作用机制，建立磁场下的微观偏析模型。目的是揭示磁场下溶质的微观偏析规律，为有效利用强磁场调控合金凝固过程微观偏析及开发与强磁场相关的凝固技术提供科学依据。

微观偏析影响合金铸坯的力学性能，腐蚀阻抗及加工性能，研究微观偏析对优化合金性能及铸造工艺具有重要的意义。在本项目的资助下，项目组系统研究了稳态磁场下影响微观偏析的各种因素变化规律，如：过冷度，固态逆扩散，枝晶粗化及固/液相线等。采用热分析法测量了磁场下Al-Cu合金熔体形核过冷度变化，发现磁场增加了合金熔体的形核过冷度，研究表明磁场增加了固液界面能以及抑制了熔体中原子扩散从而增加了形核过冷度。采用扩散偶法测量了磁场下溶质元素扩散速率变化，发现稳态磁场抑制了溶质元素的扩散速率，磁场主要通过改变扩散频率因子而非扩散活化能影响扩散系数。研究了磁场作用下枝晶粗化动力学，发现磁场作用下二次枝晶平均间距变大，磁场增加了枝晶粗化速率。耦合这些因素变化，采用微观偏析模型数值计算了有无磁场条件下Al-Cu合金非平衡二次相含量，对比了理论计算值与实验测量值，两者吻合较好。本项目研究成果为利用磁场控制合金凝固过程微观偏析行为提供了科学依据。基于本项目研究成果，项目组成员在国内外期刊上发表SCI论文13篇，申请国家专利5项，其中2项授权，培养研究生3名，圆满完成了该项目的研究计划。