Structure formation of cast aluminum-silicon alloy during thixotropic treatment

There has been growing interest in studying the formation of the structure and properties of aluminum alloys in a solid-liquid state, which is practically not used in domestic metallurgy and mechanical engineering, those at temperatures slightly higher than the eutectic, which leads to a change in the eutectic structure of the acicular type to a more dispersed equiaxial one. Therefore, the purpose of this work is to study structure formation during thixotropic treatment of an aluminum-silicon alloy, which takes place with the participation of a liquid phase, the modes of which can be adapted for thixotropic casting, which will allow changing the shape and size of eutectic crystals, which ultimately affects the mechanical properties of products. In the course of the work, the Al-12%Si alloy was studied, which underwent heat treatment at temperatures from 572 to 600 °C. During heating, isothermal holding, and cooling at a temperature above the eutectic temperature, melting and recrystallization processes occur in parallel. It was found that since the change in the state of the system is determined by a decrease in the thermodynamic potential (Gibbs energy), it is necessary to take into account the change in the volumetric energy and the change in the surface energy associated with melting (the appearance of new melt/α-solid solution and melt/Si interfaces). But it is also important to take into account that during isothermal exposure, the total surface energy will change in such a way as to minimize the final surface energy.