Modeling Crystallization Processes of a Nanomodified Binary Alloy

Abstract

A mathematical model of nonequilibrium crystallization of a binary aluminum alloy (Al-Si) with modifying refractory nanoparticles, which are the centers of nucleation of the crystalline phase, is proposed. The model describes thermodynamic processes, as well as heterogeneous nucleation and crystallization of the α-component and the β-component of a melt. The crystalline phase nucleates on the surface of nanoseeds during the undercooling of a melt. The liquidus temperature in the melt depends on the concentration of the dissolved alloying component, which is determined from the equation of the nonequilibrium lever. The α-component of the alloy crystallizes upon cooling the metal to the eutectic temperature, and the β-component of the alloy eutectically crystallizes upon further cooling. The growth rate of the crystalline phase is proportional to the undercooling. The solid volume formed around the nucleus characterizes the size of the grain structure in the solidified alloy. The numerical simulation of the solidification of the melt in a cylindrical mold is carried out. The heat transfer parameters of the melt–mold system with the environment are determined as a result of the experiments. The kinetics of heterogeneous nucleation and crystallization of the cooling melt are considered. It is found that the nucleation conditions, crystallization rate, undercooling, and solidification time significantly differ within the molding. The results lead to the conclusion that volume-sequential crystallization of the metal takes place as the melt cools. The region with the finest structure of the solidified metal is located near the mold’s wall. The size evaluation of the grain structure in the molding is in good agreement with the experimental results. The reliability of the proposed model is confirmed by comparing the results of the numerical calculations with the data of the physical experiment on the measuring temperature during solidification of the melt and studying the properties of the molding.