交流电脉冲对过共晶Al-Si合金中初生Si相偏析的作用机制  

Macrosegregation Mechanism of Primary Silicon Phase in Cast Hypereutectic Al-Si Alloys Under Alternating Electropulsing

作　　者：张利民[1] 李宁 朱龙飞 殷鹏飞 王建元[1] 吴宏景 ZHANG Limin;LI Ning;ZHU Longfei;YIN Pengfei;WANG Jianyuan;WU Hongjing(MOE Key Laboratory of Material Physics and Chemistry Under Extraordinary,School of Physical Science and Technology,Northwestern Polytechnical University,Xi􀆳an 710072,China;School of Materials Science and Engineering,Taiyuan University of Science and Technology,Taiyuan 030024,China;College of Science,Sichuan Agricultural University,Ya􀆳an 625014,China)

机构地区：[1]西北工业大学、物理科学与技术学院、超常条件材料物理与化学教育部重点实验室,西安710072 [2]太原科技大学材料科学与工程学院,太原030024 [3]四川农业大学理学院,雅安625014

出　　处：《金属学报》2023年第12期1624-1632,共9页Acta Metallurgica Sinica

基　　金：国家自然科学基金项目Nos.52074227、51801186和52130405;陕西省重点研发计划项目No.2020ZDLGY13-03。

摘　　要：通过在过共晶Al-Si合金的不同成分点及不同凝固阶段施加交流电脉冲等方法研究了电脉冲下初生Si相偏析的演变规律。结果表明,电脉冲可使高Si铝合金沿径向从边缘到中心依次形成4层梯度偏析组织:初生Si相的粗大板条状区、细化板条状区、多面体状区及近共晶组织区。相同电脉冲下合金凝固温度区间越大,初生Si偏析越显著,凝固区间超过阈值后试样中心形成近共晶组织。不同成分合金中初生相偏析都随脉冲电流密度增加先增强后减弱,但最严重偏析对应的电流密度不同。初生Si相晶核迁移是偏析的一个重要因素,结合侧壁传热受限铸型中初生Si的偏析规律,揭示了电脉冲导致初生Si相偏析的机理:初生Si相晶核在熔体内二次流作用下迁移到固/液界面前沿,在电磁斥力或其分量作用下被生长界面捕捉,从而偏析到散热、生长快的型壁及下电极附近。液相区、糊状区内对流和固/液界面前沿涡街等二次流协同作用改变了熔体内溶质分布,促进了初生Si相的连续生长和偏析,直到熔体中溶质含量接近共晶成分。Controlling the macrosegregation induced by electropulsing is of high commercial importance.This study investigates the macrosegregation of the primary Si phase in casting Al-Si hypereutectic alloys via the different solidification stages and components of alloys treated with electropulsing.Ex-perimental results show that a serious gradient macrosegregation of the primary Si phase occurs,and four types of primary Si regions are formed:coarse plate-like,refined plate-like,and fine polygon primary Si,as well as a eutectic structure.The wider the solidification temperature range,the more serious the macrosegregation.A near-eutectic structure occurs at the center of ingots when the solidification temperature range exceeds a certain threshold.With an increasing current density of electropulsing,the segregation degree of primary Si increases initially and then decreases for different Al-Si hypereutectic alloys,but the current density with regard to the most serious segregation is closely related to the Si content.Furthermore,it is proved that the migration behavior of primary Si particles plays an important role in macrosegregation.A special casting experiment under the condition of limited heat flux along the radial direction was performed to clarify the macrosegregation mechanism of primary Si under electropulsing.After nucleation during the solidification process,the primary Si particles move to the front of the solid-liquid interface due to secondary flow in bulk liquid and then are easily captured due to the electromagnetic repulsive force or its component.The force flow in the bulk liquid and mush zone and the secondary flow in front of the solidliquid interface make obvious solute redistribution and promote the growth of the primary Si phase,which is maintained until the solute concentration in the bulk liquid approaches the eutectic composition.

关 键 词：初生Si相 电脉冲 宏观偏析 二次流 熔体对流 

分 类 号：TG113.12[金属学及工艺—物理冶金]