State Key Laboratory of Advanced Special Steels, Shanghai University, Shanghai, 200072, P. R. China.
SIMAP-EPM-Madylam/CNRS, Enshmg, BP 95, 38402, St Martin d'Heres Cedex, France.
Sci Rep. 2017 Apr 3;7:45834. doi: 10.1038/srep45834.
Understanding the macrosegregation formed by applying magnetic fields is of high commercial importance. This work investigates how static magnetic fields control the solute and primary phase distributions in four directionally solidified alloys (i.e., Al-Cu, Al-Si, Al-Ni and Zn-Cu alloys). Experimental results demonstrate that significant axial macrosegregation of the solute and primary phases (i.e., AlCu, Si, AlNi and ZnCu phases) occurs at the initial solidification stage of the samples. This finding is accompanied by two interface transitions in the mushy zone: quasi planar → sloping → quasi planar. The amplitude of the macrosegregation of the primary phases under the magnetic field is related to the magnetic field intensity, temperature gradient and growth speed. The corresponding numerical simulations present a unidirectional thermoelectric (TE) magnetic convection pattern in the mushy zone as a consequence of the interaction between the magnetic field and TE current. Furthermore, a model is proposed to explain the peculiar macrosegregation phenomenon by considering the effect of the forced TE magnetic convection on the solute distribution. The present study not only offers a new approach to control the solute distribution by applying a static magnetic field but also facilitates the understanding of crystal growth in the solute that is controlled by the static magnetic field during directional solidification.
研究外加静态磁场控制定向凝固过程中溶质和初生相宏观偏析的行为具有重要的商业价值。本工作研究了外加静态磁场对四种定向凝固合金（Al-Cu、Al-Si、Al-Ni 和 Zn-Cu 合金）中溶质和初生相（AlCu、Si、AlNi 和 ZnCu 相）分布的影响。实验结果表明，在样品的初始凝固阶段，溶质和初生相（AlCu、Si、AlNi 和 ZnCu 相）会发生显著的轴向宏观偏析。这一现象伴随着糊状区中两个界面转变：准平面→倾斜→准平面。磁场下初生相宏观偏析的幅度与磁场强度、温度梯度和生长速度有关。相应的数值模拟结果表明，由于磁场和热电磁（TE）电流之间的相互作用，在糊状区中会产生单向的 TE 磁对流模式。此外，提出了一个模型来解释这种特殊的宏观偏析现象，该模型考虑了强制 TE 磁对流对溶质分布的影响。本研究不仅为通过施加静态磁场控制溶质分布提供了一种新方法，也有助于理解在定向凝固过程中静态磁场控制下溶质的晶体生长行为。
