Al-Ti-B细化工业纯铝凝固组织演变过程数值模拟

Numerical simulations of solidification microstructure evolution process for commercial-purity aluminum alloys inoculated by Al-Ti-B refiner

采用耦合群体动力学方法与元胞自动机方法建立了细化处理条件下铝合金凝固微观组织演变的数值模型.该模型考虑了a-Al的非均匀形核过程、晶粒的初始球形长大以及之后的枝晶生长过程.利用建立的模型模拟了Al-5Ti-1B中间合金细化工业纯铝凝固组织演变过程.结果表明:形核初始阶段,熔体中存在充足数量的有效形核粒子, a-Al形核率随着熔体过冷度的增大逐渐增高;形核开始不久后, a-Al的异质形核过程由熔体中有效形核粒子数量控制,直到再辉发生,形核停止.模拟分析了中间合金添加量以及熔体冷却速度对工业纯铝凝固组织演变过程的影响,模拟结果与实验结果相符,验证了模型的准确性.

Solidification microstructure of aluminum alloy has a great influence on the properties of the casting.An aluminum alloy with the structure of fine equiaxed grains has low casting defects and presents excellent mechanical properties.Recently,chemical inoculation by adding grain refiner is the technique most extensively used to achieve a fine,equiaxed grain structure of Al alloy in the industrial production.In order to investigate the detailed solidification microstructure evolution of the alloy,many numerical models have been proposed.Cellular automaton method is one of the powerful tools for simulating the morphology evolution of detailed grains in the solidification process of alloy.However,the present cellular automata model has a shortcoming,that is,its calculation of the nucleation rate is based on the experimental number density of grains.In this work,a population dynamics-cellular automaton model is developed for describing the solidification microstructure evolution of the inoculated aluminum alloy.The model takes account of the heterogeneous nucleation of a-Al nucleus,the initial spherical growth of a-Al grains and the dendritic growth process.The model is used for simulating the solidification microstructure evolution of the commercial-purity aluminum(CPAl)inoculated by Al-5Ti-1B master alloy.The results indicate that the heterogeneous nucleation process of a-Al can be divided into the two stages.In the early stage of nucleation,there are enough effective particles in the melt.The nucleation rate of a-Al increases with the increase of the undercooling of the melt.After a short time,the nucleation of a-Al is dominated by the number density of the effective particles in the melt.Nucleation process stops when the recalescence takes place.The effects of the additive amount of Al-5Ti-1B master alloy and the cooling rate of the melt on the solidification microstructure of the CP-Al are investigated by using the established model.The final solidification structures of CP-Al are predicted.And a comparison between the predicted results and the experimental ones shows that they are in good agreement with each other.