Papers by Keyword: Rotating Magnetic Field

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Authors: Sonja Steinbach, Johannes Dagner, Marc Hainke, Jochen Friedrich, Lorenz Ratke
Abstract: A quantitative understanding of the effect of fluid flow on the microstructure of cast alloys is still lacking. The application of time dependent magnetic fields during solidification offers the possibility to create defined flow conditions in solidification processing. The effect of rotating magnetic fields (RMF) on the microstructure formation in cast Al-alloys (Al-7wt.%Si, Al-7wt.%Si- 0.6wt.Mg) is studied experimentally and numerically. The forced fluid flow conditions result in pronounced macrosegregation effects and affect microstructural parameters. With increasing fluid flow the primary dendrite spacing decreases whereas the secondary dendrite arm spacing increases. The experimental analysis is supported by a rigorous application of numerical modeling with the software package CrysVUn.
Authors: Yasushi Ido, Keisuke Asakura, Hitoshi Nishida
Abstract: Behaviors of both micrometer-size nonmagnetic abrasive particles and micrometer-size magnetic particles in a magnetic fluid are investigated by using the discrete particle method which is based on the simplified Stokes dynamics. Sheet-like clusters of nonmagnetic particles and sheet-like clusters of magnetic particles alternately appear one after another in the axis direction when the flow velocity is small.
Authors: Olga Budenkova, Anne Noeppel, Jenő Kovács, Arnold Rónaföldi, András Roósz, Anne Marie Bianchi, Florin Baltaretu, Mabel Medina, Yves Fautrelle
Abstract: A numerical investigation of directional solidification of Al-7wt.%Si alloy stirred by a rotating magnetic field is compared with experimental results. Experimental study of such process has revealed periodical macrosegregation in axial direction of the samples in the shape of a “Christmas tree”. Similar macrosegregation pattern is obtained in simulations for the two values of magnetic field. Numerical simulations have shown also that formation of the periodical structure depends not only on the external conditions but on the permeability of the mushy zone.
Authors: Wen Chang Lang, Bai Zhong Wu, Bin Gao
Abstract: Based on the principle of the control of magnetic field on arc spot motion, a compact and multi-function magnetic field steered arc source has been designed in this paper. The rotating magnetic field generator driven by small DC motors or AC motors has been also equipped behind the base of the target materials of magnetic field steered arc source. The magnet yoke fixed on shaft will be driven by the motors so as to promote the rotation of permanent magnets which are rationally distributed on magnet yoke. The different distribution of permanent magnets will produce the rotating magnetic field with different configuration structures and then the purpose of multi-control mode can be achieved. Meanwhile, the dynamic rotating magnetic field with different configurations have been also produced in this design through employing the simple and compact arc source as well as the permanent magnet with different distributions in order to improve the discharge form of arc spots, control the trajectory of arc spots, improve the utilization of target materials and the uniformity of etching as well as reduce or inhibit the emission of large particles. At the same time, the high-quality film can be also prepared so as to realize the arc spot control with various forms in an arc source, satisfy the different demands and expand the application of arc ion plating.
Authors: Arnold Rónaföldi, Jenő Kovács, András Roósz
Abstract: The effect of flow on the structure of solidified alloys can be investigated by the unidirectional solidification of alloys stirred with a magnetic (magnetohydrodynamics – MHD) method. This MHD method is a rotating magnetic field (RMF)-type. The paper deals with the melt flow generated by this RMF.
Authors: Zhao Chen, Xiao Li Wen, Chang Le Chen
Abstract: The solidification behaviors of Sn-Zn alloy under rotating magnetic field (RMF) with different magnetic intensities and different rotating frequencies were investigated, and the velocity of the convection induced by RMF was calculated. It is found that the trunk length of the precipitated phase reduces with the increase of magnetic intensity and rotating frequency, and the precipitated-phase distribution is more uniform. The tangential rate increases with increasing the magnetic intensity and rotating frequency, and reaches the maximum value at about 0.55r0. All the results indicate that the solidification microstructure is attributed to the effect of RMF on the nucleation, temperature fluctuation and fluid convection in the solidification process. It predicts that RMF presents obvious advantages on controlling solidification microstructure.
Authors: Zhao Chen, Xiao Li Wen, Chang Le Chen
Abstract: Solidification behaviour of Pb-Bi alloys under rotating magnetic field (RMF) was investigated experimentally to understand the effect of the frequency of RMF on the nucleation and growth behaviour. It was found that, as the increase of the rotating frequency, the grains are fragmented and refined gradually until a transition from columnar to equiaxed microstructures happens at a rotating frequency of 40 Hz. Moreover, the Bi concentration of the primary phase decreases and macrosegregation is eliminated effectively with RMF. These are due to the effect of RMF on the nucleation, growth and fluid flow in the solidification process.
Authors: Yi Si
Abstract: In the present paper, based on Bi-containing hypereutectic Al-20%Si alloy, a rotating magnetic field was used, the microstructures of the alloy have been observed and analyzed by optical microscope and scanning electronic microscope, and its wear-resisting property was measured. The influence mechanism of rotating magnetic field on the microstructures and properties of the alloy has been discussed. Research results show that exerting a rotating magnetic field in the hypereutectic Al-20%Si alloy drastically decreases the amount of primary Si phase, only some tiny bulk Si exist and the amount of needle eutectic Si increase. The dendrite-like primary α-Al appears at the same time. With the increase of stirring rate of rotating magnetic field, the change way of eutectic Si shape is coarse needle→tiny needle→coarse needle; the rotating magnetic field can change the nonuniform distribution of Bi induced by Bi local decentralization. With the increase of stirring rate of rotating magnetic field, the change way of Bi shape in upper part microstructures of the alloy is large bulk→short rodlike→big globular→small globular, Bi local decentralization is changed into uniform distribution; In addition, exerting a rotating magnetic field in the hypereutectic Al-20%Si alloy can increase wear-resisting property of the alloy.
Authors: Galina Kasperovich, Sonja Steinbach, Lorenz Ratke
Abstract: Gradient annealing experiments of a near-eutectic AlCu30 alloy with artificial stirring induced by a rotating magnetic field (RMF) of 6 mT were performed. The specific surface area of the primary phase was measured on metallographic sections perpendicular to the sample axis with a fixed amount of fraction solid. The variation of the specific surface area with fluid flow is compared to flow free experiments: the specific surface area varies as the inverse cube root of annealing time if no RMF is applied, but varies as an inverse forth root at 6 mT. The experimental procedure and results are presented in detail and discussed with models of convective coarsening of dendrites.
Authors: Johannes Dagner, A. Weiß, Marc Hainke, Gerhard Zimmermann, Georg Müller
Abstract: A global numerical model of a Bridgman furnace is developed and validated. The model includes heat transfer due to radiation and conduction in a stationary setup. The rotating magnetic field (RMF) device mounted on the facility is implemented into the model also. A numerical study on the flow field caused by the axial non-uniform RMF and natural convection is performed, helping to get a better understanding of the convective conditions during the directional solidification experiments.
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