摘要
针对电磁悬浮条件下过共晶Al-18at%Si合金凝固组织中初生(Si)相的表层偏聚现象,结合有限元方法对悬浮液滴温度场和流场进行研究,旨在揭示初生(Si)相偏聚的物理机制.结果表明,Al-Si合金熔体在冷却过程中温度梯度和反向双涡流状流场是初生(Si)相在样品表层偏聚的主要因素,进而导致悬浮样品内部Si含量降低.同时,随初生(Si)相偏聚现象的加剧,内部形成共晶(Si)相形貌从针状转变为球状和短棒状.此外,在有限元计算中引入示踪粒子模拟了不同尺寸粒子在Al-Si合金熔体中的运动,并结合实验,发现不同粒径的初生(Si)颗粒均向样品表层迁移,粒径越大所需迁移时间越短.进一步地,对悬浮凝固样品显微硬度进行研究,发现由于初生(Si)相的表层偏聚使得样品表层具有超高硬度,约为内部显微硬度的13倍,从而提供了一种制备外硬内韧复合材料的新途径.
To reveal the physical mechanism of primary silicon(Si) segregation,the temperature and flow field of levitated droplets were studied using finite element simulation,aiming at the segregation phenomenon of primary Si phase in hypereutectic Al-18at%Si on the sample surface at electromagnetic levitation condition.The results show that the temperature gradient and reverse double eddy current flow field are the main factors that cause the primary Si phase to converge on the sample’s surface,which leads to the decrease in Si content in the levitated sample.Simultaneously,the morphology of the eutectic Si phase changed from needle to spherical and short rod with the increase of primary Si phase segregation.Additionally,tracer particles were introduced into the finite element calculation to simulate the movement of particles of different sizes in the Al-Si alloy melt.Combined with the experiment,it is found that the primary Si particles of different sizes migrate to the surface of the sample,and the smaller the particle size,the longer the migration time.Furthermore,the microhardness of the sample was studied.It was found that the primary Si phase was concentrated on the surface of the sample,which made the surface of the sample have ultrahigh hardness,about 13 times the internal hardness,thereby providing a new way to prepare composites.
作者
刘文斌
梁琛
张彭超
王海鹏
LIU Wen Bin;LIANG Chen;ZHANG Peng Chao;WANG Hai Peng(School of Physical Science and Technology,Northwestern Polytechnical University,Xi’an 710072,China)
出处
《中国科学：技术科学》
EI
CSCD
北大核心
2023年第1期41-52,共12页
Scientia Sinica(Technologica)
基金
国家重点研发计划(编号:2018YFB2001800)
国家自然科学基金(批准号:51734008)资助项目。
关键词
过共晶AL-SI合金
电磁悬浮
凝固
hypereutectic Al-Si alloy
electromagnetic levitation
solidification
