铸造参数对2024铝合金半连铸过程中宏观偏析影响的数值模拟（英文）

Effects of Casting Parameters on Macrosegregation in 2024 Alloy During Direct-chill Casting Based on Numerical Simulation

采用考虑了浮游晶运动的拓展连续模型计算大尺寸2024铝合金半连铸铸锭的宏观偏析。模型中宏观的传质、传热、动量传输方程与Scheil-Gulliver微观凝固模型相互耦合。通过9个算例计算铸造参数(铸锭尺寸、铸造速度、浇注温度以及二冷区冷却强度)对宏观偏析的影响,并讨论了铸造参数对形成宏观偏析传输机制的影响。结果表明,铸造参数直接影响熔池的形状和尺寸进而影响最终偏析形态。其中,铸锭尺寸和铸造速度是最主要的影响因素。更大的铸锭尺寸通常意味着更慢的冷却速度,以及更深和更宽的熔池,从而导致铸锭中心更严重的宏观偏析。增加铸造速度则将显著地增加熔池的深度,因而更大的铸造速度将导致更严重的宏观偏析。而熔池的深度随浇注温度的增加仅轻微增加,故浇注温度对宏观偏析的影响不如前二者敏感。

The extended continuum mixture model considering the floating grain motion was applied to calculate the macrosegregation of large-size billet of 2024 aluminum alloy during direct-chill(DC)casting.Transport equations of mass,momentum,species and heat were solved simultaneously with the Scheil-Gulliver micro-model.The effects of casting parameters(billet size,casting speed,casting temperature and intensity of secondary cooling zone)on macrosegregation were calculated in nine cases.Influence of casting parameters on the transport mechanisms for macrosegregation formation was discussed.The results demonstrate that the processing parameters directly affect the shape and dimension of the sump,thereby affecting the final segregation patterns.The billet size and casting speed play the most important roles.A larger billet size usually means a slower cooling rate and a deeper and wider sump,which results in severe segregation in the billet center.The sump depth dramatically increases with the increase of the casting speed.Therefore,higher casting speed promotes greater macrosegregation.Nevertheless,the sump depth increases slightly with increasing the casting temperature.