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Calculation on Viscosity of Al-Cu Liquid Alloys
Abstract
The review on models on the concentration dependence of the dynamic viscosity of binary melting alloys is presented in this paper. It is analyzed the existing literature data on the experimental investigation for viscosity for Al-Cu system. The calculated data on viscosity for Al-Cu liquid alloys compared with literature data.
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Six different theoretical equations are compared in the present paper with experimental data, measured for 28 binary liquid metallic systems. General conclusions are drawn on the ability of the different theoretical models to describe the concentration and temperature dependence of the viscosity of liquid alloys. A new equation is derived, being able to predict the viscosity in multi-components alloy even if the viscosities of the pure components are not known.
A large body of published data is presented on the viscosity of alloy liquids at compositions corresponding to elements, intermetallic compounds and eutectics. In all these cases, with the exception of liquids showing strong association and in particular of good glass-formers, it is found: that the melting point viscosity is well matched by the Andrade formula; and that the temperature-dependence of the viscosity above the melting point is Arrhenius, with approximately constant pre-exponential viscosity, and with activation energy proportional to the melting point. For glass-forming systems the temperature-dependence of the viscosity is best fitted by the Vogel-Fulcher-Tammann equation, and a procedure is outlined for estimating the parameters in the equation. Some qualitative correlations are demonstrated for the composition-dependence of isothermal viscosity in binary alloys.
We present a general view of discontinuous structural phase transition of liquid metal and alloys induced by the temperature based on the viscosity analyses for more than ten kinds of liquid metal and alloys. Differential Scanning Calorimetry (DSC) experiment also verified the existence of phase transition. The viscosity model consisting of liquid structure model and fluid cluster diffusion model are proposed to explore the nature of discontinuity of structural phase transition. In addition, the viscosity expression within a phase zone has also been brought forward. This present work makes a beneficial attempt at exploring viscosity as an experimental method for studying liquid-liquid (L-L) phase transition.
Viscosity measurements on Al80Cu20 molten alloys were made using an oscillating cup viscometer. Two abnormal viscosity change points were found at 780 and 850 °C. The eject temperatures were chosen based on the temperature dependence of viscosity. Amorphous alloys produced with different eject temperatures show a different crystallization temperature. We found that the trend of viscosity changes with temperature is more important than the viscosity itself in the glass formation process.
In this work, a simple predictive scheme has been developed for estimating the viscosity of molten metallic alloys as a function of temperature and composition. Based on the parameters of a two constant equation for the viscosity-temperature relationship of pure components, the mixture rules proposed herein do not entail any additional constants and thus only pure component values are needed.The present method predicts nearly 1000 individual viscosity values for 29 binary alloys and one ternary alloy with an average error of 10.5%.
Temperature dependences of kinematic viscosity n of liquid Al100-x-Cux alloys (x = 0.0, 10.0, 17.1, 25.0, 32.2, 40.0 and 50.0 at.%) were measured. A technique based on registration of the period and the decrement of damping of rotating oscillations of a cylindrical crucible with a melt was used. Viscosity was calculated in low viscous liquids approximation. Measurements were carried out in vacuum in crucibles of BeO with a temperature step of 30°C and isothermal expositions of 10 to 15 minutes during both heating up to 1100-1250°C and subsequent cooling. We have discovered branching of heating and cooling curves v(T) (hysteresis of viscosity) below temperatures depending on the copper content: 950°C at 10 and 17.1 at.% Cu, 1050°C at 25 and 40 at.% Cu, 850°C at 32.2 at.% Cu. For samples with 10 and 17.1 at.% Cu the cooling curve ‘returns’ to the heating one near 700°C. An abnormally high spreading of results at repeated decrement measurements was fixed at heating of the alloy containing 50 at.% Cu above 1000°C. During subsequent cooling the effect disappeared. Isotherms of kinematic viscosity have been fitted for several temperatures.
The dynamic viscosity measurements are performed for Al–Cu alloy melts with different compositions using an oscillating-cup viscometer. The results show that the viscosities of Al–Cu alloy melts increase with the copper content increasing, and also have a correlation with the correlation radius of clusters, which is measured by the high-temperature X-ray diffractometer. It has also been found that the fragilities of superheated melts (M) of hypereutectic Al–Cu alloys increase with the copper content increasing. There exists a relationship between the fragility and the structure in Al–Cu alloy melts. The value of the M reflects the variation of activation energy for viscous flow.
The partial and integral enthalpies of mixing in liquid Al-Si and Al-Cu alloys were determined by high-temperature isoperibolic calorimetry at 1750+/-5 and 1590+/-5, respectively. The thermodynamic properties of Al-Si melts were also studied by electromotive force method in temperature range 950-1270 K. The partial and integral excess Gibbs free energies of mixing in liquid Al-Si and Al-Cu alloys were also calculated from literature data on thermodynamic activity of aluminium. The comparison of our experimental results with literature data has been performed.
Densities and thermal expansion coefficients of liquid Al–Ag and Al–Cu alloys were measured using the technique of electromagnetic levitation. This technique involves producing shadow images of the sample from which the volume is calculated by an image processing algorithm.
Data was obtained at temperatures above the melting point. The concentration dependence of density and thermal expansion was studied for both systems. It was found for Al–Ag and Al–Cu that both density and thermal expansion can be related to a negative excess volume and its temperature coefficient.
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