Numerical Simulation and Experimental Validation of Nondendritic Structure Formation in Magnesium Alloy Under Oscillatio
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SINCE the discovery of the rheological behavior of nondendritic structure semisolid slurries by M.C. Flemings in the early 1970s,[1] effort has been made to understanding nondendritic structure formation under an external field. Nondendritic structure formation is known to be a microscale phenomenon that involves the thermal and compositional fields, melt convection, the motion of the crystal, and complex coupling processes. It has great interest in research and for industrial applications.[2] In the solidification process, melt convection[3] is mainly induced by stirring, rotation, vibration, pouring, density differences between the different components, or the temperature difference between different regions. It plays a key role in the nondendritic crystal growth, including in dendrite fragmentation[4,5] and freckle formation.[6,7] The movement of the grains
ANSHAN YU, XIANGJIE YANG, KUN YU, XIUYUAN SUN, and ZIXIN LI are with the School of Mechanical and Electrical Engineering, Nanchang University, Nanchang 330031, P.R. China and also with the Key Laboratory of Near Net Forming in Jiangxi Province, Nanchang 330031, P.R. China. Contact e-mail: [email protected] HONGMIN GUO is with the Key Laboratory of Near Net Forming in Jiangxi Province and also with the Department of Materials Science and Engineering, Nanchang University, Nanchang 330031, P.R. China. Manuscript submitted January 8, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
in the melt is another important phenomenon in the solidification process of an alloy and affects the microstructure and the composition distribution of the casting.[8] For example, in the formation of equiaxed structures, it is caused by the interaction between moving dendrites[9] and has been observed in situ using X-ray diffraction imaging techniques.[10] By now, numerous solidification models have been developed for microscale analysis, such as the phase field,[11] cellular automata,[12] enthalpy,[13] and level-set[14] methods. These models deal with the effect of the diffusive environment on the growth of the dendrites and help understand the transport of heat and solute in the solid–liquid interface as well as the factors that control the stability and the shape of the dendrite tip.[15] Some recent models have incorporated the effect of melt flow on the growth of the dendrites. For example, large-scale simulations have been carried out by coupling cellular automata with the lattice Boltzmann[16] and the phase field with the lattice Boltzmann method.[17] However, the motion of the dendrites was ignored in most models. To overcome this disadvantage, rigid body motion and rotation has been introduced in the growth of dendrites in alloys. Liu et al.[3] used the cellular automata-lattice Boltzmann method to simulate the growth and motion of the equiaxed dendrites. Medvedev et al.[18] simulated a single dendrite solidification with motion and rotation with the phase-field and lattice Boltzmann methods. Rojas et al.[2] and Takaki et al.[19] used the phase-field lattice Boltzmann method to simulate the grow
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