Research On Correlation Between Viscosity And Structure Of Liquid Al-In And Ag-Sn Alloys

Research on the structure and physical properties of liquid metals and alloys is fundamental problems in the field of physics of metals and condensed matter. Liquid metals have been studied for more than half a century, however, more work must be carried out to enrich theoretical models of liquid metals for complicated structure and properties. Viscosity measurements on liquid monotectic Al-In alloys were made using an oscillating cup viscometer in present paper. Investigation focus on the temperature and composition dependence of liquid viscidity, the correlation between liquid viscosity and liquid-liquid phase transition, elevated viscidity of melts. Furthermore, elevated-temperature X-ray diffractormeter was used to study the structure and the correlation between viscidity and structure of liquid Al-In alloys. Liquid viscidity and structure of Ag-Sn system are also being investigated and viscosities were calculated by empirical formulation to obtain the excess viscosity. The zone maps were made according to the viscidity behavior of two systems of liquid alloys.There are immiscible gaps in monotectic alloys because of liquid-liquid separation, which result in segregation after solidification. It was found in present work that viscosities changed suddenly when liquid-liquid separation occur and there was little deviation of the sudden change temperature from bi-liquidus temperature.The viscosities of liquid Al-In alloys exist sudden change above the liquidus temperature of120K approximately, which shows that liquid microstructure change promptly above liquid-liquid phase separation temperature and fluctuation of composition, concentration and energy occur. According to the turning temperature of viscosities, areas above the bi-liquidus can be divided into two zones and the zone map of Al-In was obtained. In a homogeneous liquid phase region, the temperature dependence of liquid viscosity corresponds to Arrhenius equation. The fitting parameters, A, is related to flow unit’s size and the cube root of I/A is proportional to the flow unit’s size. When the mass percentage Al and In approaches in the I area adjacent to bi-liquidus, flow unit’s size and viscous activation energy reach the maximum values. However, the melts with In-rich and Al-rich composition have less flow unit’s size and viscous activation energy. In the II area far from bi-liquidus the flow unit size and the viscous activation energy decrease with increasing In content.The structure parameters of Al-90wt.%In derived from X-ray diffraction experiments show that order of melt strengthen with decrease of temperature. Sudden changes of the liquid structure parameters occur at1273K which has a deviation of1.6%from the temperature of sudden change of its liquid viscosity. Thus, it is suggested that In-rich and Al-rich clusters appear to prepare for nucleation of liquid-liquid phase transition from1273K to liquid-liquid phase transition temperature. In general, the performance of liquid viscosity can reflect the transition of liquid structure.Ag-Sn alloy is a kind of alloys with complicated liquid-solid phase transition including not only the peritectic reaction, but also the eutectic reaction. The various types of solid phases indicate that the liquid structure may have abundant behavior. Investigation on liquid viscosity of Ag-Sn alloys reveals sudden changes of viscosity during the cooling process. The melts can be divided into2to4temperature zones due to the sudden change temperature and the zone maps were obtained. The flow unit’s size and viscous activation energy develop with the types of solid microstructure that shows the close correlation between liquid and solid.Liquid viscosities of the Ag-Sn system at1248K were calculated using two empirical formulas. Comparison the calculated results with the experimental results show that the divergence of radii of ions and atomic mass influent the liquid viscosity more than the mixing enthalpy of melts, especially for liquid alloys with Sn content less than70at%. The absolute values of excess viscosity are great with Sn content less than70at% both in calculations and experiments. It indicates that the existence of intermetallic compound and solid solution with high content of the second phase strengthen the order of liquid alloys.Liquid structure of Ag-Sn alloys were studied by X-ray diffraction experiments. According to the structure evolution of liquid Ag86Sn14alloy with temperature, the ordered structures strengthen with the decrease of temperature. Due to the performance of structure parameters, the melt can be divided into three zones. The size of clusters, the atomic number within clusters, the coordination number, the nearest-neighbor distance are quite different in three zones. The turning points of liquid structure occur in1123K,1268K, which are close to that of viscosity,1123K and1263K. The structure parameters of liquid Ag38Sn62alloys change suddenly at1038K approach to the sudden change temperature of liquid viscosity. For liquid Ag16Sn84alloys, weak shoulder peaks were found on the right side of the first main peaks of intensity curves and structure factor curves, which become weaker with the decrease of temperature. The shoulder peaks indicate there are covalent bonds of Sn-Sn in liquid Ag16Sn84. The liquid structure parameters of Ag16Sn84exist transition at723K deviated of4.2%from the turning point of liquid viscosity. Experimental researches on liquid Ag-Sn system reveal the close correlation between liquid viscosity and structure.In general, the present work manifests that the liquid viscosity has close correlation to liquid structure. The transition temperature of liquid structure can be obtained through researching the evolution of liquid viscidity. The melts can be divided into several zones due to the turning points of structural transition. The temperature and composition dependence of liquid structure have close relation to solid microstructure.