Evaluation of the thermodynamic properties of mixing of the bismuth-antinomy system

Although it is known that there is complete miscibility in both the solid and liquid phases in the bismuth-antimony system, there is some uncertainty in the solidus line . The results of GLAZOV obtained by equilibration and quenching, and of CAMPBELL give values about 20 K higher than the compilation of HANSEN, and GLAZOV concludes that precise solidus data are difficult to obtain by quenching. In view of these uncertainties, the additional information available from heats of mixing in the liquid state has been combined with HANSEN's phase diagram to evaluate the thermodynamic properties of the system

Simulation of flow in a continuous galvanizing bath: Part II. Transient aluminum distribution resulting from ingot addition

The coupled phenomena of momentum, heat, and mass transfer were simulated in order to predict and to better understand the generation and movement of intermetallic dross particles within certain regions of a typical galvanizing bath. Solutions for the temperature and aluminum concentration can be correlated with the solubility limits of aluminum (Al) and iron (Fe) to determine the amount of precipitated aluminum in the form of Fe2Al5 top dross. Software developed by the Industrial Materials Institute of the National Research Council of Canada (IMI-NRC), including k-\u3b5 turbulence modeling for heat and mass transfer, was adapted for the simulation of a sequence of operating parameters. Each case was modeled over a period of 1 hour, taking into account an ingot-melting period followed by a nonmelting period. The presence of an ingot significantly changes the temperature distribution and also results in important variations in the local aluminum concentration, since the makeup ingot has a higher aluminum concentration. The simulation showed that during the ingot melting, the total aluminum concentration is higher at the ingot side of the bath than at the strip exit side. The region below the ingot presents the highest aluminum concentration, whereas lower aluminum concentrations were found in the region above the sink roll, between the strip and the free surface. It was shown that precipitates form near the ingot surface because this region is surrounded by a solution at 420 \ub0C, which is lower than the average bath temperature of 460 \ub0C. When no ingot is present, the total aluminum concentration becomes much more uniform and decreases with time at a constant rate, depending on the coating thickness. This information is of major significance in the prediction of the formation of dross particles, which can cause defects on the coated product.Peer reviewed: YesNRC publication: Ye

Simulation of flow in a continuous galvanizing bath : Part I. Thermal effects of ingot addition

A numerical analysis has been developed to simulate the velocity and temperature fields in an industrial galvanizing bath for the continuous coating of steel strip. Operating variables such as ingot addition, line speed, and inductor mixing were evaluated in order to determine their effect on the velocity and temperature distribution in the bath. The simulations were carried out using high-performance computational fluid-dynamics software developed at the Industrial Materials Institute of the National Research Council Canada (IMI-NRC) in solving the incompressible Navier-Stokes equations for steady-state and transient turbulent flow using the k-\u3b5 model. Cases with and without temperature-dependent density conditions were considered. It was found that the strip velocity does not alter the global flow pattern but modifies the velocities in the snout, near the strip, and near the sink and guide rolls. At a low inductor capacity, the effect of induced mixing is small but is considerably increased at the maximum inductor capacities used during ingot-melting periods. When considering the thermal effects, the flow is affected by variations in density especially near the inductors and the ingot, while little effect is observed near the sheet-and-roller region. Thermal effects are also amplified when the inductor operates at high capacity during ingot melting. The simulations allow visualization of regions of varying velocity and temperature fields and clearly illustrate the mixed and stagnant zones for different operating conditions.Peer reviewed: YesNRC publication: Ye

Deformation behavior of semi-solid A356 Al-Si alloy at low shear rates: The effect of sample size

The rheological behavior of semi-solid metal slurries at low shear rates can be characterized by parallel plate compression tests of cylindrical discs where the height (h) is much smaller than the diameter (d) and the axial flow is assumed negligible or zero against the radial flow. In order to confirm the validity of required aspect ratio, two sets of cylindrical test samples with (h/d) of 0.4, d = 24 mm small discs, and 1.8, d = 75 mm billets, were prepared with similar microstructures. The small specimens were tested in a parallel plate squeezing flow rheometer to determine the viscosities which were compared to the viscosity values of samples (billets) with larger aspect ratios using a similar large scale apparatus. For the billets, rheocast samples, it was shown that the dendritic primary α-Al structure has the highest viscosity. The viscosity decreases when the structure comprises a rosette or globular morphology. Similar results were obtained for the discs, thixocast samples, where the specimens have similar initial microstructure. The results confirmed that for low shear rates, less than 10-2 s-1, the viscosity of semi-solid alloy is dependent mainly on the morphology of the primary particles and not the sample size. © 2006.Omid Lashkari, Reza Ghomashchi, Frank Ajersc