Simulation of the columnar-to-equiaxed transition in directionally solidified Al-Cu alloys

Surface tension of liquid metals and alloys — Recent developments

A simple method to estimate the surface tensions of binary alloys has been developed by assuming that the partial molar excess free energies are proportional to the number of nearest neighbors in both the bulk solution and in the surface itself. In order to estimate the surface tension of the alloys, excess free energies of the alloys and the surface tensions of the pure components are required. This method has been applied to ten alloys exhibiting positive, positive as well as negative, and negative deviations from ideal solution behavior. The method depends upon the reliability of the thermodynamic data for the bulk solutions, and, further, it is important to use an interpolation scheme that is consistent with the Gibbs-Duhem requirement, when the thermodynamic data are presented in tabular form as a function of composition. To accomplish this interpolation, a special calculation technique is presented.

Estimation of the surface tensions of binary liquid alloys

In this paper the available data for the measurement of viscosity of aluminium and its alloys are reviewed. Most measurements are performed with an oscillating vessel technique and the merits of this technique are discussed. The purity of the aluminium affects the measured viscosity values and we recommend a value of between 1.0–1.4 mPa·s for the pure element at the melting point. Although studies of the viscosity of aluminium alloys are limited, the effects of elemental additions to the alloy are similar to those for additions to the base metal. Thus an increase in concentration of Ti, Ni, Cr, Mn, Mg tends to increase the viscosity whereas the viscosity decreases with increasing Zn and Si concentrations. Also purification of an alloy decreases the viscosity. There is a wide variety of models ranging from those based on empiricism to thermodynamic methods. With the present quality of input data it is probably better to use a simple rather than a sophisticated model.

The viscosity of aluminium and its alloys--A review of data and models

During the last three decades, various thermodynamic databases have been compiled to be applied mainly to the calculation of phase diagrams of alloys, salts, and oxides. The accumulation and assessment of thermodynamic data and phase-equilibrium information to establish those databases is sometimes called the CALPHAD (calculated phase diagram) approach. The CALPHAD approach has been recognized as useful in various aspects of materials science and engineering. In addition to the use of thermodynamic databases for the calculation of phase diagrams, it would be very desirable to apply them to the calculation of other physicochemical quantities, such as surface tension. By doing this, not only can the Utility of databases be enlarged, but also a deeper understanding of the physical properties in question can be reached.On the basis of the concepts just mentioned, we have applied those thermodynamic databases to the calculation of the surface tension of liquid alloys and molten ionic mixtures. In these calculations, we have applied Butler's equation for the surface tension of liquid alloys. In addition, we have modified Butler's equation to be extended to molten ionic mixtures by considering the relaxation structure in the surface. These approaches will lead us to develop a multifunctional data-bank System that will be widely applicable in the evaluation of physicochemical properties of liquid alloys and molten ionic mixtures from thermodynamic data.In this article, we explain some physical modeis for the surface tension and viscosity of liquid alloys and molten ionic mixtures, in which thermodynamic data can be directly applied to evaluate these physical properties. In addition, the concept for the just-mentioned multifunctional thermodynamic data-bank System will be described by demonstrating the simultaneous calculation of phase diagrams, surface tension, and viscosity of some alloys used for new, Pb-free soldering materials.

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Use of Thermodynamic Data to Determine Surface Tension and Viscosity of Metallic Alloys

Surface tension of binary liquid alloys

Viscosity data for Al−Cu liquid alloys in the ranges of 0≤C
 L≤331 wt pct Cu and 1173≤T ≤973 K are reviewed It was found that Andrade's equation can be used to represent the variation of viscosity with temperature for a given composition, but that each of the two parameters in Andrade's equation shows no systematic variation with composition of the liquid-alloys Consequently, arithmetic averages of the parameters were used and assumed to apply to all compositions in the range 0≤C
 L ≤331 wt pct Cu Such a procedure implies that the viscosity happens to vary with composition solely because the specific volume varies with composition In order to establish the predictability of extrapolating such simple behavior, a more complex model was considered The latter model was recently presented by Kucharski and relates viscosity to the structure and thermodynamics of liquid alloys Viscosities obtained by interpolating Andrade's equation and Kucharski's model compare closely; furthermore, values obtained by extrapolations to lower temperatures also compare favorably Finally the simpler model was used to calculate the viscosity of the interdendritic liquid during solidification

R. Speiser

Papers

Estimation of the surface tensions of binary liquid alloys

Surface tension of binary liquid alloys

Viscosities of aluminum-rich Al−Cu liquid alloys

SURFACE TENSION OF ALUMINUM-RICH Al-Cu LIQUIDS ALLOYS.

Surface tension of aluminumrich Al-Cu liquid alloys