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Zhang H.T.,Northeastern University China | Cui J.Z.,Northeastern University China | Nagaumi H.,Suzhou Research Institute for Nonferrous Metals
Advanced Materials Research

In this paper, Low frequency electromagnetic field and air knife are applied simultaneously to produce large-size AA 7055 aluminum alloy ingots during DC casting. Moreover, the effects of low frequency electromagnetic field and air knife on macro-physical fields during DC casting as well as microstructure and crack in the ingots are studied and analyzed by the numerical and experimental methods. Comparison of the calculated results indicates that applying electromagnetic field can modify the flow direction and increase the velocity of melt flow and homogenize the distribution of temperature in the sump, and applying air knife can homogenize the distribution of temperature and decrease the stress and strain in the solidified ingots. Further, the microstructure of the billet is refined remarkably and the crack is eliminated by applying electromagnetic field and air knife during DC casting because of modification of the macrophysical fields. © (2014) Trans Tech Publications, Switzerland. Source

Li Z.,Shanghai JiaoTong University | Li Z.,Suzhou Research Institute for Nonferrous Metals | Luo A.A.,Ohio State University | Wang Q.,General Motors | And 2 more authors.
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

This paper investigates the fatigue properties and deformation behavior of a newly developed Mg-2.96Nd-0.21Zn-0.39Zr magnesium alloy wheel in both as-cast and T6 conditions. Compared with the as-cast alloy, the T6-treated alloy shows a significant increase in fatigue strength and cyclic stress amplitude. This is believed to be attributed to the change of defect type from porosity to oxides and the increased matrix strength in the T6 (peak-aged) condition. For the as-cast alloy wheel, fatigue failure mainly originated from the cast defects including porosity, oxide film, and inclusion at or near the sample surface. In the T6-treated alloy, however, oxides and inclusions or slip bands initiate the fatigue cracks. Solution treatment appears to reduce or eliminate the shrinkage porosity because of grain growth and dissolution of as-cast eutectic phases in the grain boundaries. The cyclic stress amplitude of the as-cast alloy increases with increasing the number of cycles, while the T6-treated alloy shows cyclic softening after the stress reaches a maximum value. The Coffin–Manson law and Basquin equation can be used to evaluate the life of low cycle fatigue. The developed long crack model and multi-scale fatigue (MSF) models can be used to predict high-cycle fatigue life of the Mg-2.96Nd-0.21Zn-0.39Zr alloys with or without casting defects. © 2016 The Minerals, Metals & Materials Society and ASM International Source

Zhang H.,Northeastern University China | Nagaumi H.,Suzhou Research Institute for Nonferrous Metals | Cui J.,Northeastern University China
Advanced Science Letters

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 200 mm diameter, cast during the conventional DC casting and the LFEC casting processes. 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. © 2012 American Scientific Publishers. All rights reserved. Source

Umeda T.,Chulalongkorn University | Umeda T.,Sahaviriya Steel Industries Co. | Thirathipviwat P.,Chulalongkorn University | Thirathipviwat P.,Showa Denko Co. | And 3 more authors.
International Journal of Cast Metals Research

Low frequency electromagnetic casting applied to high strength aluminium alloys promoted heavy stirring in direct chill melt, which prevented hot cracking of aluminium alloys never manufactured by direct chill. For instance, Al-10Zn-2·5Mg-2·3Cu alloy was able to be produced by low frequency electromagnetic casting because of the fine grain size, which is small enough, such as 50 μm, when cast into 200 mm diameter billet. It is of importance to understand the microscopic solidification behaviour to properly develop alloy design. Therefore, microsegregation in accordance with solidification progress, including the formation of various kinds of intermetallic compounds, was discussed by precise experiment through compositional analysis using microprobe mapping method. Even under a peculiar solidification condition of refined equiaxed crystals, microsegregation development was apparently similar to a columnar dendrite growth in which the initial solute pile-up was attributed to the diffusion in liquid. For heavily electromagnetically stirred billet, microsegregation was governed by back diffusion. © 2011 W. S. Maney & Son Ltd. Source

Zhang Q.,Beijing Institute of Technology | Zhao P.,Beijing Institute of Technology | Zhao P.,Suzhou Research Institute for Nonferrous Metals | Zou L.,Beijing Institute of Technology | Fan R.,Beijing Institute of Technology
Xiyou Jinshu/Chinese Journal of Rare Metals

5182 aluminum alloy is usually used as can lid due to its excellent strength and formability. For 5182 alloy, the designed strength is generally obtained by adjusting cold-rolling reduction. However, the effect trend and mechanism of cold-rolling reduction on the microstructure and mechanical properties of 5182 alloy sheet before and after baking still need systematical study. The effect of cold-rolling reduction after intermediate annealing (IA) on the microstructure and tensile properties of cold rolled and baked AA5182 aluminum alloy can lid sheets were investigated in the present study. The results indicated that as the cold-rolling reduction increased from 60% to 90%, the grain shape of cold-rolled sheets became fibrous gradually, and the strength increased due to enhanced work hardening effects. Baking at 205℃ for 20 min resulted in the recovery and the decrease of dislocations density and precipitation of β phase, and the amount of β precipitation increased with the increase of cold-rolling reduction. The strength of sheets decreased and the elongation increased significantly after baking. Meanwhile, the strength increased and elongation decreased after baking with the increase of cold-rolling reduction. The decreasing amount of strength during baking increased with cold-rolling reduction due to the reduction of Mg solid solution strengthening effect. © Editorial Office of Chinese Journal of Rare Metals. All right reserved. Source

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