Alloys Fe – Cu can be characterized as a system with immiscible components (IC). This statement is based on a weak mutual solubility in the solid state. In addition, with low carbon content, the Fe – Cu system is also stratified in the liquid state [1]. Alloys with IC have a simple phase composition of almost pure components. This determines a significant practical interest in these alloys. Certain successes have been achieved in the technology of manufacturing damping alloys of the Fe – Cu– Pb system. With optimally selected technology for their preparation, it is possible to obtain the final product combining the properties of pure alloy components in the proportion required for practical application. For example, in Fe – Cu alloys, diamagnetic copper has high electrical conductivity and thermal conductivity, and ferromagnetic iron has enhanced strength characteristics compared to copper. When structure of the alloy is organized in a certain way, it is possible to obtain either a final product with high electrical conductivity and thermal conductivity of copper, enhanced strength properties of iron, or – a hard magnetic material with ductility of copper. The ironcopper system alloys were considered in [2 – 13], in which the main attention was paid to structural studies and measurements of service properties. At the same time, the dynamics of macroand microstructure formation of alloys were not analyzed. In the present work, it was the dynamics of macrostructure formation of the solid phase enriched with iron in process of crystallization of the melt during its cooling that was studied using high-temperature viscometry. Considering the final influence of the melt cooling rate on the size and morphology of crystallizing inclusions, and a significant amount of the two-phase area, special attention was paid to thermophysical analysis of the measurement mode. Analysis of reliability of the results obtained was made by the method of viscosity measuring. Phase state of the melts of Fe – Cu system was investigated during cooling by changing the damping factor. The analysis of thermophysical processes occurring in the measurement of the damping factor was carried out. It has been established that the process of measuring the damping decrement takes place under quasi-equilibrium conditions and the cooling rate is close to zero. There are no temperature gradients, both in radius and in height. For compositions Fe50Cu50 , Fe40Cu60 , Fe30Cu70 the dynamics of precipitation of the solid phase were determined.