Study On DC Casting Of Aluminum Alloy Under The Dual-frequency Electromagnetic Fields

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.