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数值模拟了镁合金铸轧凝固中传热与流动过程,分析了铸轧速度对铸坯凝固温度场、流场的影响。制备了镁合金铸轧板坯,采用金相显微镜、扫描电镜等分析了板坯组织、形貌及成分分布特征。根据数值模拟结果与铸坯组织特征,分析了铸轧板坯中心线偏析形成过程。结果表明,镁合金铸轧速度显著影响铸轧区熔体的传热与流动过程,并决定铸坯全凝固点位置;铸轧区中熔体沿垂直轧辊面间存在强烈的热交换,铸坯沿传热反方向形成发达的柱状晶,溶质元素在凝固前沿固液界面处发生溶质再分配,Al、Zn元素在上下凝壳焊合位置富集,形成中心线偏析。
Numerical simulation of heat transfer and flow during casting and solidification of magnesium alloy was carried out. The effects of casting speed on solidification temperature field and flow field were analyzed. Magnesium alloy cast slab was prepared. The microstructure, morphology and composition distribution of the slab were analyzed by metallographic microscope and scanning electron microscope. According to the numerical simulation results and the characteristics of billet structure, the segregation of center line of cast slab is analyzed. The results show that the casting speed of the magnesium alloy significantly affects the heat transfer and flow of the melt in the roll casting zone and determines the full solidification point of the slab. In the roll casting zone, there is a strong heat exchange between the melt along the vertical roll surface, The developed columnar crystals are formed in the opposite direction of heat transfer. Solute elements are redistributed along the solid-liquid interface before solidification. Al and Zn elements are enriched in the welding position of the upper and lower crusts to form centerline segregation.