Estimation of Al – Si System Melts Structure Transformations Possibility by Thermodynamic Data

Currently, one of the promising methods of silumins mechanical properties improving is а melt thermal time treatment. Its effect is most often associated with changes in the structure during melt overheating and aging and with positive effect of these changes on alloy structure after crystallization. Although the fact that a certain close-order structure is realized in metal melts is now considered indisputable, the problem of transformations possibility in melts structure remains debatable. In previous studies, the thermodynamic parameters of Al–Si system melts were determined based on experimentally determined equilibrium compositions of the liquid and solid phases at different temperatures. The results of the analysis gave reason to assume that the structure of specified system melts may change, depending on the composition and temperature. In this paper, in order to further clarify the issue of the possibility of structural micro-heterogeneity and transformations of Al–Si system melts structure, the experimentally established valuesof components activities has been compared with the known calculated data obtained under the assumption of meltsstructure immutability. It has been established that at significantly higher than the liquidus temperature, the specified calculated parameters of the liquid phase are no longer able to adequately describe the experimentally established concentration dependences of Al–Si systemmelt components activities. This fact may indicate the possibility of changes in the structure of aluminum-silicon melts when the temperature changes. In addition, the results of analysis of experimental data on the concentration dependence of Al–Si system meltsintegral enthalpy of mixing do not contradict the idea of possibility of structure changingof this system melts when the silicon content in them changes. The results obtained provide grounds for further research of Al–Si system meltsstructure changespossibilityusing the analysis of temperature-concentration dependences of their associative composition and experimental research of temperature dependences of structurally sensitive properties (for example, electrical resistance).