【作者】 李吉相；

【导师】 崔建忠； 赵志浩；

【作者基本信息】 东北大学 ， 材料加工工程， 2009， 硕士

【摘要】 本课题是教育部青年教师基金项目(双频组合磁场作用下铝合金半连续铸造过程中熔体凝固行为研究)的部分内容,其目的是开发一种双频组合磁场铝合金DC铸造新工艺,以达到同时改善铸锭表面质量和内部组织的目的。本文的研究内容包括：设计制作了双频磁场实验设备,通过改变中低频线圈的放置位置以及施加电磁屏蔽,设计出了三种不同的实验设备。考察了不同实验方案条件下,低频磁场、中频磁场以及双频磁场对铸锭质量的影响。分析了铝合金半连续电磁铸造中低频磁场、中频磁场和双频组合磁场对改善铸锭表面质量和铸态组织的作用原理。通过实验分析和讨论得出以下结论：(1)两个双频线圈上下放置时,两个线圈形成的磁场不能同时集中作用于结晶器内石墨环附近的铝合金的熔体,放置在下部的低频线圈离结晶器较远,致使单独施加低频磁场对铸态组织的影响不明显；施加中频磁场可以改变DC铸造过程中熔池液面形态,增大熔池中液面的凸起高度,提高铸锭表面质量,减小铸锭皮下偏析层厚度。(2)两个线圈里外放置时,两个线圈形成的磁场可以同时集中作用于结晶器内石墨环附近的铝合金的熔体；单独施加低频磁场可以很好的细化铸态组织,单独施加中频磁场可以细化铸锭边部组织,但铸锭中部组织粗大；中、低频磁场同时施加时,由于中频磁场的热效应削弱了低频磁场对铝合金铸锭组织的细化效果,所以双频磁场对铸锭组织的改善作用较低频磁场弱。(3)两个线圈里外放置并在中频线圈内施加电磁屏蔽时,单独施加低频磁场可以很好的细化铸态组织；同时施加中低频磁场时,铸锭的铸态组织与单独施加低频磁场的铸态组织相差不大,电磁屏蔽可以很好的消除中频磁场的热效应对铸锭铸态组织的不利影响。综上所述,在常规DC铸造过程中施加双频磁场时,通过合理地布置双频线圈位置,适当地施加磁场屏蔽,可以显著细化铸态组织,提高铸锭表面质量,达到提高铝合金铸锭质量的目的。更多还原

【Abstract】 This subject is a part work of "Research on solidification behaviors during semi-continuous casting of aluminum alloy under dual-frequency combined electromagnetic fields", which is supported by Young Teachers Fund Project of the Ministry of Education. The main purpose of this work is to develop a new casting process under dual-frequency electromagnetic fields, and then to obtain aluminum alloy ingots with high metallurgical quality.The content of this study includes the design of three kinds of dual-frequency electromagnetic combined fields DC casting sets by changing the location of two inductors and introducing electromagnetic shielding. The effects of the low- frequency electromagnetic field, intermediate-frequency electromagnetic field, and dual-frequency electromagnetic fields on the ingot’s quality were investigated under the three kinds of sets. The principles of the electromagnetic fields improving the as-casting microstructure and surface quality was analyzed.The main results are as followings:(1) When the low frequency inductor was placed under the intermediate frequency inductor, the electromagnetic fields formed by the two inductors can’t force on the melt near the graphite ring in the DC casting process simultaneously because of the long distance from the low-frequency inductor to the mould, so that the effect of low-frequency electromagnetic field on the as-cast structure was not obvious. The intermediate-frequency electromagnetic field can change the surface shape of melt in the DC casting process, so the surface quality of the ingots was improved and the segregation layer of the ingots reduced with the application of intermediate-frequency electromagnetic field.(2) When the low frequency inductor was placed in inner of the intermediate frequency inductor, the electromagnetic fields formed by the two inductors can force on the melt near the graphite ring in the DC casting process simultaneously. As only the low-frequency electromagnetic field was applied in the DC casting process, the as-casting microstructure of the whole ingot was fined obviously. As only the intermediate-frequency electromagnetic field was applied in the DC casting process, the as-casting microstructure in the edge of the ingot was fined obviously, but the microstructure in center was coarse. As the low-frequency electromagnetic field and intermediate-frequency electromagnetic field were applied simultaneously in the DC casting process, the refining effect of the low-frequency electromagnetic field on cast microstructure was weakened by the thermal effect, so the effect of dual-frequency electromagnetic fields on improving the as-casting microstructure was not better than that of low-frequency electromagnetic field.(3) When the low frequency inductor was placed in the inner of the intermediate frequency inductor, and an electromagnetic shielding was used. As only the low-frequency electromagnetic field applied in the DC casting process, the as-casting microstructure of the whole ingot was fined obviously. As the low-frequency electromagnetic field and intermediate-frequency electromagnetic field were applied simultaneously in the DC casting process, the as-casting microstructure was as fine as that of only applying low-frequency electromagnetic field. So the electromagnetic shielding can eliminate the negative effect of the intermediate-frequency electromagnetic field on the as-casting microstructure effectively.In summary by reasonable placement of the two inductors and suitable electromagnetic shielding in the DC casting process the dual-frequency electromagnetic fields can improve the as-casting microstructure and the ingot surface quality effectively.更多还原