中文摘要：

以AZ91D合金为例，模拟研究镁合金凝固时的溶质分布情况，着重定量分析过冷度ΔT对枝晶尖端前沿最高溶质浓度、枝晶干轴对称中心溶质浓度、枝晶尖端溶质扩散层厚度以及溶质偏析比的影响。模拟结果表明：贫 Al 区主要集中于一次枝晶干和二次枝晶臂的轴对称中心，过冷度ΔT越大，枝晶尖端前沿溶质浓度c＊L越高，枝晶干中心溶质浓度＊Sc 越高，枝晶尖端前沿溶质扩散层厚度δ越小，偏析比 SR越大，微观偏析越严重，其具体关系分别为c＊L1＞c＊L2＞c＊L3＞c＊L4、＊S1c ＞＊S2c ＞＊S3c ＞＊S4c 、δ1＜δ2＜δ3＜δ4和SR1＞SR2＞SR3＞SR4。

英文摘要：

Based on the KKS model which couples the phase field, concentration field and temperature field, the phase-field model for the magnesium alloys with hcp structure was developed, taking AZ91D magnesium alloy for example, the solute distribution during the metal solidification was simulated, the effects of supercooling （ΔT） on the highest solute concentration in front of the dendrite tip, the solute concentration value in the axis center of dendrite arm, the thickness of solute diffusion layer of aluminum in front of dendrite tip and solute segregation ratio were studied emphatically and quantitatively. The simulation results show that the zone of poor Al distributes in the axisymmetric center of primary dendrite arms secondary dendrite arms, the larger the supercoolingΔT is, the higher the concentration maximum value c＊L in front of the dendrite tip is, the higher the concentration value ＊Sc in the axis center of dendrite arm is, the smaller the boundary thicknessδof concentration in front of the dendrite tip is, the bigger the segregation ratio SR is and the severer the microsegregation is. The relationships are c＊L1＆gt;c＊L2＆gt;c＊L3＆gt;c＊L4 , ＊S1c ＆gt; ＊S2c ＆gt; ＊S3c ＆gt; ＊S4c , δ1＆lt;δ2＆lt;δ3＆lt;δ4 and SR1＆gt;SR2＆gt;SR3＆gt;SR4, respectively.