Macro segregation formation mechanism of the primary silicon phase in directionally solidified Al-Si hypereutectic alloys under the impact of electric currents
Macro segregation formation mechanism of the primary silicon phase in directionally solidified Al-Si hypereutectic alloys under the impact of electric currents
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DOI：
10.1016/j.actamat.2015.07.002
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发表时间：
2015-09-15
期刊：
影响因子：
9.4
通讯作者：
Zhai, Qijie
中科院分区：
文献类型：
--
作者：
Zhang, Yunhu;Miao, Xincheng;Zhai, Qijie
理解通过施加电流形成的宏观偏析具有很高的商业重要性。本文研究了电流对定向凝固Al-20.5wt%Si过共晶合金中溶质分布的控制作用。实验结果表明，在凝固初期，初生硅发生了严重的宏观偏析。这伴随着糊状区中的两个界面转变：准平面-向上V形->准平面。相应的数值模拟结果显示，由于糊状区的电流畸变，出现了涡环流型。考虑强制流动对溶质分布的影响，可以充分解释这种特殊的宏观偏析现象。在样品的初始生长，强制流动产生了一个严格的溶质交换之间的糊状区和散装熔体，并鼓励初生硅不断沉淀和偏析。随着熔体中溶质含量逐渐接近共晶点，初生硅的析出大大减少。最终，在初始定向生长中观察到初生硅相的显著偏析。本研究不仅提出了一种新的方法来控制溶质分布通过施加电流通过产生的强制流，它也有利于理解潜在的晶粒细化机制和晶体生长的溶质，由电流控制。(C)2015 Acta Materialia Inc.由爱思唯尔有限公司出版。保留所有权利。
Understanding the macro segregation formed by applying electric currents is of high commercial importance. This paper investigates how electric currents control the solute distribution in the directionally solidified Al-20.5 wt%Si hypereutectic alloy. Experimental results show that a severe macro segregation of the primary silicon phase occurs at the initial solidification stage of the samples. This is accompanied by two interface transitions in the mushy zone: quasi planar - upwards V-shaped -> quasi planar. The corresponding numerical simulations present a vortex ring flow pattern as a consequence of the electric current distortion in the mushy zone. The peculiar macro segregation phenomenon can be fully explained by considering the effect of the forced flow on the solute distribution. At the initial growth of the samples, the forced flow generates a rigorous solute exchange between the mushy zone and the bulk melt and encourages the primary silicon to continuously precipitate and segregate. As the solute content in the bulk melt gradually approaches the eutectic point, the precipitation of primary silicon is profoundly reduced. Eventually, a significant segregation of the primary silicon phase is observed in the initial directional growth. The present study not only presents a new approach to control the solute distribution by applying an electric current through a generated forced flow, it also facilitates the understanding of the underlying grain refinement mechanism and the growth of crystals in the solute that are controlled by the electric currents. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.