Pb-Sn合金定向凝固斑点偏析的数值模拟

为了探究二元合金垂直定向凝固过程中斑点偏析的形成过程,建立了定向凝固条件下速度场、溶质场及温度场耦合求解的数学模型,并利用该模型模拟了Pb-10wt%Sn合金圆柱形铸锭内的定向凝固过程。结果表明,造成斑点偏析的流动起源于液相区而非糊状区内,富含溶质的流体不断向糊状区通道处流动聚集,并通过糊状区从液相区持续补充通道内的流动。凝固结束后在铸锭内部形成了细长的溶质富集通道,顶部斑点分布在以铸锭半径的1/2为半径的圆弧附近,这一结果由实际生产铸锭的斑点偏析情况得以验证。

Numerical Simulation of Freckle Formation During Directional Solidification of Pb-Sn Alloy

In order to investigate the formation of freckle during vertical directional solidification of binary alloys,a mathematical model for the coupled solution of velocity field, solute field and temperature field was established under directional solidification. This model was used to simulate the directional solidification process of Pb-10 wt%Sn alloy in a cylindrical ingot. The simulation results show that the flow causing freckle formation originates from the liquid region rather than the mushy zone. The solute-rich fluid continuously converges toward the channels of mushy zone and continues to replenish the flow in the channel from the liquid region through the mushy zone. Some elongated solute enrichment channels are formed inside the ingot after solidification, and these top freckles are located near the arc with a radius of R/2. This result was also verified by the freckle formation in actual ingots.