铝合金枝晶生长形貌数值模拟研究

采用宏微观耦合方法对铝合金枝晶生长形貌进行模拟计算。由于对整个试样进行微观计算存在困难 ,所以采取的方案是整体计算温度场 ,而微观组织计算则是在试样中心区域选取其中一个单元进行 ,该单元的微观组织模拟被简化为二维计算。采用较大的网格和时间步长Δt计算宏观温度场 ,当选取的单元温度降到液相线以下时 ,在一个宏观时间步长Δt内 ,采用小网格和小时间步长δt对该单元进行微观组织计算 ,宏观、微观计算交替进行。形核过程采用了高斯分布模型 ,生长过程由相场方程来控制。微观区域内的初始温度分布由周围的宏观单元温度插值得到 ,界面过冷包含热过冷、成分过冷和曲率过冷。溶质分布则用混合溶质守恒方程来描述。为了描述二次枝晶的产生 ,在相场模型中引入了噪声。模拟结果与实际浇注的试样的金相结果以及其他学者的结果进行了比较。

Research on Numerical Simulation of Dendritic Growth Morphology of Aluminum Alloy

Numerical simulation of dendritic growth morphology is studied by using a macro micro coupled method. Since it is difficult to compute the microstructure of a whole casting, a scheme is adopted that the temperature field is calculated on the whole casting while the microstructure computation is carried out by selecting a cell in the central region of the casting. The growth of the dendrite is controlled by the solution of the phase field equation. The initial distribution of the temperature in the micro domain is obtained by interpolating the temperature of the cells near the selected cell and the interface undercooling is considered to be the sum of thermal, solute and curvature effects. The distribution of the solute is described by using the mixed solute conservation equation and the noise is introduced to produce the side branches. The simulation results are compared with those obtained experimentally.