离心渗铸工艺中铝熔体在SiC多孔介质内的渗流传热过程特征及最弱环损伤模型

针对离心力场中铝熔体在SiC多孔介质内的渗流传热现象,考虑离心力对渗流传热过程的影响,根据局部非热平衡假设建立了多孔介质渗流传热模型。采用全隐格式TDMA算法和第一类迎风差分方法对渗流过程的温度场进行了数值计算。研究分析了不同复合层厚度下离心渗透过程中的流场和温度场瞬态变化规律。计算结果表明,在渗透区域,熔体与SiC颗粒存在着一定温差,而在渗透前沿,这种温差相对较大。渗流速度变化存在两个十分明显的阶段,渗流速度较高且急剧下降的初始渗透阶段以及渗流速度相当平稳的后续阶段。渗流速度的这种瞬态变化规律主要是多孔介质内流体流动与离心压力相互作用的结果。渗透初期形成的紊流状态,是导致熔体卷吸空气、使复合材料内部形成气孔的主要原因之一。选择合适的工艺参数对于确保铸件质量是十分关键的。

INFILTRATION OF MOLTEN ALUMINUM AND HEAT TRANSFER IN CENTRIFUGAL CASTING PROCESSES

In this paper, molten aluminum flow with heat transfer through SiC porous media in a centrifugal force field was described with a mathematical and physical model. The implicit TDMA Algorithm and the first kind of first-order upwind difference were employed to solve the conservation equation associated with appropiate boundary conditions. The distribution of molten aluminum velocity and its pressure, the temperature profiles of fluid and porous media in a centrifugal force field were examined for different conditions. The results show that the local temperature of the fluid phase is different from that of the solid phase in the front edge of the infiltrated region. The temperature difference between the fluid and solid phases increases with the SiC volume fraction and angular velocity, and decreases with the time of infiltration. The infiltration of the molten aluminum through SiC porous media depends mainly on the angular velocity of the centrifugal force field. SiC volume fraction has a strong effect on the velocity and pressure distribution of the molten aluminum.