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研究

Effects of casting parameters on macrosegregation in 2024 alloy during direct-chill casting based on numerical simulation

摘要:

本文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。通过九个算列计算铸造参数（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，并详细讨论了铸造参数对形成宏观偏析传输机制的影响。研究结果表明，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。

Abstract:

The extended continuum mixture model with considering the floating grains 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 (e.g. billet size, casting speed, casting temperature and intensity of secondary cooling zone) were calculated in nine cases. Influence of the transport mechanisms for macrosegregation formation dependent on casting parameters were discussed in detail. Our study demonstrated that the processing parameters directly impacted the shape and dimension of the sump, thereby affecting the final segregation patterns. The billet size and casting speed played the mostly important roles. A larger billet size usually means a slower cooling rate, a deeper and wider sump, which results in the severer segregation in the billet center. The sump depth dramatically increases with the increase of the casting speed. Therefore, higher casting speed promotes greater macrosegrgation. Nevertheless, the sump depth increases slightly with increasing of casting temperature.