Besides diffusion and capillary, convection which is unavoidable under terrestrial condition has remarkable effects on the microstructure evolution during solidification. In this study, a phase-field lattice-Boltzmann model, accelerated by state-of-the-art parallel-adaptive mesh refinement algorithm, is solved to investigate the morphological evolution of the Mg-Gd dendrite under convection. The lengths of the dendrite primary arms are quantified to analyze the asymmetric dendrite patterns under convection. The effects of the multiple factors including the orientation angle, the flow intensity, and the undercooling are elucidated, and the relation between the length ratios and the three independent factors is established through multiple regression analysis. The upstream-downstream arm length difference and the included angle between the primary arms are characterized to illustrate the effect of convection on the evolution of the Mg-Gd dendrite. The 3D morphological selection, together with algorithm performance tests, is further discussed to elucidate the change of morphological symmetry under different growth conditions and to demonstrate the robustness of the numerical scheme. Deep understanding of the synergy between convection-induced solute transport and undercooling-driven growth, which largely determines the morphological selection, can assist guidance for the prediction and control of the magnesium alloy microstructures.

中文翻译：

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对流作用下镁枝晶微观结构的数值研究：枝晶对称性的变化


除了扩散和毛细作用外，在陆地条件下不可避免的对流对凝固过程中的微观结构演变也有显著影响。在本研究中，求解了由最先进的并行自适应网格细化算法加速的相场晶格玻尔兹曼模型，以研究对流作用下 Mg-Gd 枝晶的形态演变。量化树突初级臂的长度以分析对流下的不对称树突图案。阐明了方向角、流动强度和过冷度等多个因素的影响，并通过多元回归分析建立了长度比与 3 个独立因素之间的关系。表征了上下游臂长差和主臂之间的夹角，以说明对流对 Mg-Gd 枝晶演化的影响。进一步讨论了 3D 形态学选择以及算法性能测试，以阐明不同生长条件下形态对称性的变化，并证明数值方案的鲁棒性。深入了解对流诱导的溶质传输和过冷驱动生长之间的协同作用，这在很大程度上决定了形态选择，有助于指导镁合金微观结构的预测和控制。