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论文类型：期刊论文

发表时间：2018-09-01

发表刊物：ACTA MATERIALIA

收录刊物：SCIE

卷号：156

页面范围：287-296

ISSN号：1359-6454

关键字：Magnesium alloys; Zinc; 4D imaging; Dendrite orientation transition; Morphology transition

摘要：Dendritic microstructural evolution during the solidification of Mg-Zn alloys was investigated as a function of Zn concentration using in situ synchrotron X-ray tomography. We reveal that increasing Zn content from 25 wt% to 50 wt% causes a Dendrite Orientation Transition (DOT) from a six-fold snow-flake structure to a hyper-branched morphology and then back to a six-fold structure. This transition was attributed to changes in the anisotropy of the solid-liquid interfacial energy caused by the increase in Zn concentration. Further, doublon, triplon and quadruplon tip splitting mechanisms were shown to be active in the Mg-38 wt%Zn alloy, creating a hyper-branched structure. Using the synchrotron tomography datasets, we quantify, for the first time, the evolution of grain structures during the solidification of these alloys, including dendrite tip velocity in the mushy zone, solid fraction, and specific surface area. The results are also compared to existing models. The results demonstrate the complexity in dendritic pattern formation in hcp systems, providing critical input data for the microstructural models used for integrated computational materials engineering of Mg alloys. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.