Experimental and Modeling Studies of the Lamellar Eutectic Growth of Mg-Al Alloy
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EUTECTIC alloys can form a variety of different two-phase microstructures during the liquid/solid phase transformation. Because of their superior mechanical properties associated with a fine-scale composite microstructure, eutectic alloys have attracted much attention in the realm of materials science.[1] In addition, the use of eutectic materials as in situ composites is of great interest to metallurgists.[2] Two important parameters of eutectic microstructures are the volume fractions of the two eutectic phases and the lamellar spacing, which affect the mechanical properties of eutectic materials significantly. As the volume fractions can be controlled to some extent by alloy composition, the eutectic lamellar spacing is affected mostly by the imposed growth conditions.[3] Following the pioneering analysis of Jackson and Hunt,[4] who established a classic eutectic theory relating eutectic spacing with interface undercooling and growth velocity, various additional theoretical models have been developed for eutectic growth under different growth conditions, which are also consistent with previous experimental results.[5–7] SHOU-MEI XIONG, Professor, and MENG-WU WU, Doctoral Candidate, are with the Department of Mechanical Engineering, State Key Laboratory of Automobile Safety and Energy, Tsinghua University, Beijing 100084, P.R. China. Contact e-mail: smxiong@ tsinghua.edu.cn Manuscript submitted November 24, 2010. Article published online August 31, 2011 208—VOLUME 43A, JANUARY 2012
Numerical modeling and simulation has been developed rapidly as a powerful tool for simulating and predicting the time-dependent microstructure evolution during various solidification processes. Based on a reliable reproduction of eutectic growth and the corresponding structure features, numerical modeling has the capability to study the kinetics of the solidification interface during eutectic growth and to investigate the effects of process parameters quantitatively on eutectic structures. Among those numerical modeling techniques, the phase field (PF) method can predict and depict the evolution of complex solidification structures effectively. Since the previous works by Steinbach and Pezzolla,[8] the PF method has been used extensively to simulate the phase transformation processes of multiphase and multielement systems.[9–11] However, because of the requirement of a small cell size with respect to the thickness of the solid/liquid interface and the consequent significant computational power, the PF method is limited to a small calculation domain. Another drawback of the PF method is related to the large number of parameters involved in the solution of the constitutive equations. These parameters are difficult to determine for the simulation of accurate physical eutectic growth of real materials. The cellular automaton (CA) method is another way to predict a wide range of realistic phenomena associated with dendritic or nondendritic microstructure formation. By introducing stochastic factors, the CA method has been used extensively for si
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