合金凝固过程中晶粒尺寸和形貌演变的预测

利用合金凝固热力学原理，考虑形核和长大因素，建立了预测晶粒尺寸的理论模型，利用该模型对近液相线半连续铸造6061铝合金的晶粒大小进行了计算，所得结果与实验吻合.在所计算的几个条件中，最大误差小于7μm.通过对凝固过程中液固界面法向生长的扰动分析，得出球形晶粒周边主导波长及对应于一定波数的临界晶粒直径表达式.利用此关系可以很好地解释球晶生长及其向一定形貌的枝晶转变的条件及机理；对于分析凝固组织中不同形貌晶粒的形成及演化具有参考价值；对于半固态合金组织性能预测及其制备工艺优化具有实际意义.

Prediction of the Grain Size and the Morphology Evolution of Alloys in Solidification Process

A theoretical model on the grain size prediction was established according to the thermodynamics of the alloy solidification and consideration on the factors of the nucleation and grain growth. The grain size of the near liquidus semicontinuous casting 6061 aluminum alloy was calculated by using the model. The calculated results are well consistent with the experimental ones with the maximum error less than 7μm. Through the analysis of the growing disturbance along the normal direction to the liquid solid interface during the solidification， a equation of the critical grain diameter corresponding to a certain wave number and the dominant wavelength surround the spherical grains were obtained. The spherical grain growth and its transformation conditions and mechanism of dendritic grains with specific type were well explained by these expressions， which is of great significance to the study on the formation and evolution of the grains with different morphologies， and to the prediction of microstructures and properties of semisolid alloy as well as the processing optimization.