(上海大学 材料科学与工程学院 上海市现代冶金及材料制备重点实验室，上海 200072)
摘 要: 使用有限元耦合元胞自动机模型预测水平单向凝固实验中Al-4.5%Cu(质量分数)合金试样的温度场和微观凝固组织。晶体形核和枝晶生长动力学模型分别采用Rappaz连续形核模型和Kurz-Giovanola-Trivedi(KGT)模型简化形式，基于纯扩散条件，采用KGT模型简化公式计算生长参数。结果显示：数值模拟可以较准确地预测柱状晶向等轴晶转变(CET)位置和等轴晶晶粒尺寸，但因模拟未考虑晶核的运动，激冷等轴晶区的模拟有较大偏差。模拟和实验结果都证明过热度显著影响Al-Cu合金的凝固组织，过热度低于20 ℃条件下可以获得全等轴晶组织，否则会出现柱状晶；过热度50 ℃以上的试样CET位置几乎不发生变化。
关键字: Al-Cu合金；元胞自动机；凝固过程；柱状晶向等轴晶转变；热模拟
（Shanghai Key Laboratory of Modern Metallurgy and Materials Processing,
School of Materials Science and Engineering, Shanghai University, Shanghai 200072, China）
Abstract:The temperature field and the grain structure of Al-4.5%Cu (mass fraction) alloy in horizontal directional solidification process were predicted using a cellular automaton (CA) coupled with finite-element (FE) model. The Rappaz model was adopted to calculate the nucleation. And the Kurz-Giovanola-Trivedi (KGT) model was used to describe the growth kinetics of dendritic tips. The growth parameters of Al-4.5%Cu alloy were calculated using simplified KGT formula, which was derived based on the pure diffusion condition. The results show that the position of the columnar to equiaxed transition (CET) and the size of equiaxed grains can be simulated reasonably. However, large deviation of the simulated result exists in the chill zone as the movement of nucleus is not considered. The simulated and experimental results prove that the superheat greatly influences the solidification microstructures of Al-Cu alloy. Full equiaxed grains can be obtained if superheat is lower than 20 ℃, otherwise columnar grains will be observed. When the superheat is above 50 ℃, the positions of CET are no longer changed.
Key words: Al-Cu alloy; cellular automaton; solidification process; columnar to equiaxed transition; thermal simulation
