The effect of the electromagnetic vabration on the microstructure, segregation, and mechanical properties of As-cast AZ8
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M alloys are the lightest structural alloys and have attracted increasing attention in recent years. The application of magnesium alloys, especially for cast and wrought products, is increasing due to their excellent properties such as high specific strength, high specific rigidity, and low density.[1–4] Direct-chill (DC) casting was invented in the 1930s and found its practical application as a common way to produce ingots and billets for further deformation processing. There are a significant number of publications in the literature pertaining to the technology of DC casting for aluminum alloys.[5–8] However, for magnesium and its alloys, increasing attention has been paid to studying the process of DC casting since it was first developed in Germany and the United States.[9–12] Although the DC casting process has been used to produce aluminum alloy billets, and more recently magnesium alloy billets, there is still much work necessary to improve the billet quality. During the last decade, the demand for higher quality cast products, especially with respect to surface quality, chemical homogeneity, and fine-grain structure, called for new fundamental research in the casting process. Among the various approaches studied, the use of the electromagnetic fields is considered important because it can have a significant effect due to the fact that it does not contact the melt. To improve the billet surface quality, a technology of electromagnetic casting was developed that applied electromagnetic fields to pinch the liquid metal and to realize the casting process in the absence of a mold.[13] To refine the grain size, an electromagnetic stirring field was used during the casting because it generated a forced convection inside the melt and led to a significant reduction of the grain size in the solidified product.[14,15] Yang et al. reported the SHIJIE GUO, Graduate Student (Postdoctoral Candidate), QICHI LE, Associate Professor, YI HAN, Graduate Student (Postdoctoral Candidate), ZHIHAO ZHAO, Assistant Professor, and JIANZHONG CUI, Professor, are with the Department of Key Laboratory of Electromagnetic Processing of Materials, Ministry of Education, Northeastern University, Shen Yang, 110004 P.R. China. Contact e-mail: [email protected] Manuscript submitted September 2, 2005. METALLURGICAL AND MATERIALS TRANSACTIONS A
refined solidification structure and the enhanced mechanical properties of 25Cr-20Ni-Fe-C alloy in centrifugal casting by applying a steady magnetic field.[16] However, their works mainly concentrated on the effects of a single magnetic field on castings. In 1993, Vives introduced a new technology of electromagnetic vibration for continuously casting aluminum alloy.[17,18,19] In his system, a stationary magnetic field (DC field) and an alternating magnetic field (AC field) were simultaneously applied during the continuous casting of aluminum alloy. With the interaction between the applied magnetic fields and the induced current, vibration and stirring were generated inside the metal melt, respectively.[17] He also reported that t
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