Analysis of Features of Heat Transfer during Crystallization of Aluminum Alloy Granules in a Water and Water–Steam Environment

Abstract

The results obtained using the developed mathematical model of a detailed change in the temperature field and the phase transitions during cooling and crystallization of a melt droplet under cooling in the water and water–steam environment are analyzed. The presented mathematical model not only allows one to establish temperature fields in the droplet or granule body but also determines the velocity of motion of a droplet in a coolant at each specific instant of time, the intensity of heat removal, the cooling rate, and the melt crystallization rate at different points in the volume. The aforementioned ultimately makes it possible to predict dendrite sizes and the properties and phase composition of a material of synthesized granules. The mathematical model has been tested in granulation of aluminum superalloys (D1 and D16 alloys of the Al–Cu–Mg system and V95 and V96Ts alloys of the Al–Zn–Mg–Cu system) obtained by centrifugal spraying of melt and the drop method upon cooling in a water environment. The rate of crystallization in natural samples has been measured by analyzing the dendritic parameter of the material structure. The mathematical model has demonstrated a high degree of convergence of the results of simulation modeling and the results of real experiments for production of granules. The model has yielded, in particular, fairly accurate results of the formation of granules at ultrahigh crystallization rates without a “steam jacket,” i.e., a vapor layer appearing between the granule body and the coolant, reducing the heat removal intensity and preventing the growth of the crystallization rate owing to the lower thermal conductivity of water vapor.