Papers by Keyword: Low Frequency Electromagnetic Casting

Abstract: A comprehensive multiphysics model has been developed to describe the effect of the low frequency electromagnetic field (LFEM) [1, on solidification in the hot-top Direct-Chill (DC) casting [ of round aluminium alloy billets. The volume averaged equations and the rigid solid phase assumption are assumed for fluid flow and heat transfer [. The electromagnetic induction equation for the field imposed by the coil is solved using the diffuse approximate method (DAM), structured in axial symmetry with Gaussian weight function, 6 polynomial basis and 9 nodded domains. The heat, mass, and momentum transfer equations are solved in primitive variables by meshless [ method using 5 nodded domains of influence and 5 scaled multiquadrics radial basis functions, using collocation. Explicit time stepping is used. Pressure-velocity coupling is performed by the fractional step method. The effects of intensity and frequency of the LFEM [ on the velocity and temperature fields is investigated. A comparison of the calculated results with different LFEM field process variables with that of the conventional hot-top DC casting process indicates that the velocity patterns, the temperature profiles, and the shape of the sump could be modified remarkably.

Abstract: Hot tearing and cold cracks are major defects during direct chill (DC) casting of large sized ingots of high strength aluminium alloys. In order to solve these problems, based on a low frequency electromagnetic casting (LFEC) process, a new technology, electromagnetic casting with the application of an air blade (EMA) was developed. In the present work, this new technology was used to prepare large sized AA7055 aluminium alloy ingots and the effects of the low frequency electromagnetic field and the air blade on macro-physical fields, microstructure and cracking are studied by numerical and experimental methods. The results show that applying an electromagnetic field can modify the flow direction, increase the velocity of melt flow and homogenize the distribution of temperature in the sump. Applying an air blade can homogenize the distribution of temperature and decrease the stress and strain in the solidified ingot. Furthermore, the microstructure of the ingot is refined remarkably and cracking is eliminated by simultaneously applying the electromagnetic field and the air blade during DC casting.

Abstract: In order to understand the effect of casting temperature on the low frequency electromagnetic casting process, 200mm billets of an Al-Zn-Mg-Cu alloy were produced, the microstructure was analyzed and the temperature field was measured during the casting process. The experimental results showed that low frequency electromagnetic casting process has an evident grain refining effect on aluminum alloy and casting temperature is not a sensitive parameter for this process, which can tolerate a large range of casting temperature. In the range of 710 to 750 °C, casting temperature does not show significant effect on the microstructure.

Abstract: Grain refinement is quite important for producing 7050 alloy billet especially in large scale. Low frequency electromagnetic casting (LFEC) process was used to make 7050 aluminum alloy Φ500 mm billets and study the effect of electromagnetic field on the microstructure. The sound Φ500 mm billets of 7050 alloys without any grain refiner can be successfully prepared by the LFEC process. The results show that low frequency electromagnetic field has a significant grain refining effect on 7050 alloy and can effectively eliminate feather grain structure. The microstructures of LFEC ingot from the border to the center of the cross section are all equiaxed grains and are finer and more uniform than that of conventional direct chill (DC) cast billets. The LFEC process also shows a strong power to eliminate hot tearing during casting large sized billet of high strength aluminium alloy.

Abstract: Low frequency electromagnetic casting (LFEC) process was used to make 7050 aluminum alloy 162mm ingots and study its effect on the as-cast microstructure. Effects of electromagnetic field parameters such as frequency and current intensity on microstructures were systemically investigated. The results showed that LFEC has a significant grain refining effect on 7050 alloy. The microstructures of LFEC ingot from the border to the center of the cross section are all equiaxed or nearly equiaxed grains which are much finer and more uniform than those of DC cast ingot. It was also found that electromagnetic field frequency and current intensity play important roles on the microstructure refinement. The discussion was mainly focused on the mechanism of grain refinement by LFEC process.

Abstract: Grain refinement is quite important for producing 7050 alloy ingot especially in large scale. Low frequency electromagnetic casting (LFEC) process was used to make 7050 aluminum alloy Φ310 ingots and study the effect of electromagnetic field and grain refiner on the microstructure of 7050 alloy ingots. The results showed that both grain refiner and low frequency electromagnetic field can result in some grain refinement of 7050 alloy. However, the low frequency electromagnetic field shows more remarkable grain refinement. For the grain refined alloy by grain refiner, further significant grain refinement can be achieved with the application of low frequency electromagnetic field. The finest microstructure was achieved by combining the applications of both grain refiner and electromagnetic field.

Abstract: 7050 aluminum alloy ingots were produced by low frequency electromagnetic casting (LFEC) and direct chill casting (DC) respectively. As-cast microstructures and homogenization behaviors of LFEC and DC ingots were investigated experimentally. The optical microscope and DSC analyses shown that the grain size of LFEC ingot was finer and the content of constituents and eutectic structure was less than that of DC ingot. Accordingly, the homogenization behaviors of the LFEC and DC ingots were significantly different. The remnant constituents of LFEC ingot were less in content and smaller in size than that of DC ingot after homogenization at 480°C for various lengths of time. Similar to the dissolving of constituents, the LFEC ingot exhibited faster diffusion kinetics of alloying elements from grain boundary to inner. The concentrations of Cu, Mg and Zn inside grain of LFEC ingot after homogenization for 12 h were 2.4%, 2.2% and 6.5% respectively, but the DC ingots had not reach the level even for 48 h.

Abstract: Low frequency electromagnetic casting is a new developed technology that appears in the recent years. In this paper, a comprehensive mathematical model has been developed to describe the interaction of the multiple physics fields during LFEC (low frequency electromagnetic casting) process. The model is based on a combination of the commercial finite element package ANSYS and the commercial finite volume package FLUENT, with the former for calculation of the electromagnetic field and the latter for calculation of the magnetic driven fluid flow, heat transfer and solidification. Moreover, the model has been verified against the temperature measurements obtained from one 7XXX aluminum alloy billet of 200mm in diameter, during the LFEC casting processes, respectively. There was a good agreement between the calculated results and the measured results. Further, the effects of electromagnetic frequency on fluid flow, temperature field and solidification during LFEC process have investigated numerically by using the mathematic model. The choosing criterion of the electromagnetic frequency during LFEC process has been used in order to obtain the best structure of the billets by analyzing the effects of fluid flow and temperature field on the solidification process in the presence of electromagnetic field.

Abstract: A comprehensive mathematical model has been developed to describe the interaction of the multiple physics fields during the conventional DC casting and LFEC (low frequency electromagnetic casting) process. The model is based on a combination of the commercial finite element package ANSYS and the commercial finite volume package FLUENT, with the former for the calculation of the electromagnetic field and the latter for the calculation of the magnetic driven fluid flow, heat transfer and solidification. Moreover, the model has been verified against the temperature measurements obtained from two 7XXX aluminum alloy billets of 200mm diameter, cast during the conventional DC casting and the LFEC casting processes. In addition, a measurement of the sump shape of the billets were carried out by using addition melting metal of Al-30%Cu alloy into the billets during casting process. There was a good agreement between the calculated results and the measured results. Further, comparison of the calculated results during the LFEC process with that during the conventional DC casting process indicated that velocity patterns, temperature profiles and the sump depth are strongly modified by the application of a low frequency electromagnetic field during the DC casting.