Jie Yu Zhang

Measuring and Modeling of Viscosities of Selected CaO-MgO-Al2O3-SiO2 Slags

Viscosities of selected quaternary CaO-MgO-Al2O3-SiO2 slags have been measured by rotary cylinder method up to a temperature of 1875K. 9 slag compositions have been selected in the composition range 40.04-50.64 wt. % CaO, 6.40-7.12 wt. % MgO, 22.84-41.73 wt. % Al2O3 and 10.25-20.70 wt. % SiO2. The effect of increasing temperature was investigated and it was shown that viscosity decreased, as expected, with increasing temperature. The viscosity increases with increasing the ratios of CaO/Al2O3, and following by a decrease with further increasing the ratios of CaO/Al2O3. An application of Iida’s viscosity model has been made. The Iida model gave good consistency with the measured viscosity values.

Experimental Investigation of the Phase Equilibria of Al-Zn-Ti System in Al-Rich Corner at 400 °C

The phase equilibria in Al-rich corner of the Al-Zn-Ti ternary system at 400 °C were determined by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS) and X-ray powder diffraction (XRD). The results showed that this section consisted of three ternary-phase regions, namely, L+(Al)+τ, Ti2Al5+τ+(Al) and Ti2Al5+TiAl3+(Al). The XRD patterns and EDS confirmed that a Ti2Al5-structured phase with containing 4 at.% Zn was stable at 400 °C. Furthermore, the ternary new phase (τ phase) was identified in samples and in equilibrium with (Al), Ti2Al5 and liquid, respectively.

Three-Dimensional Numerical Simulation of Metal Flow in the Initial Stage of a Twin-Roll Strip Casting Process

A three-dimensional mathematical model has been developed to study turbulent fluid flow, heat transfer and free surface profile in the initial stage of the twin-roll casting strip pool by a commercial software ProCAST. The coupled set of governing equations for mass, momentum and energy balance was solved with the finite element method. The free surface profile of the pool was treated with the Volume of Fluids (VOF) approach. A straight nozzle of metal delivery system has been chosen in the Twin-roll strip casting process. The filling sequences, flow patterns and corresponding temperature profiles in the metal pool of a vertical twin-roll strip casting process were simulated in this study. The calculated results provided a valuable basis for the optimization of process parameters and metal delivery system during the initial pouring stage of twin-roll strip casting.

Thermodynamic Studies on Selective Oxidation of Nb, P and C in Dephosphorization of Low Niobium Hot Metal

The main problem with the efficient utilization of Nb resource in the Boyan Obo Ore lies in the selective oxidation of [Nb], [P] and [C]. In this work, thermodynamic studies have been conducted to determine the conditions of selective oxidation of [Nb], [P] and [C] in low niobium hot metal in the process of oxidizing dephosphorization. The thermodynamic condition for dephosphorization was determined as: The condition for retaining Nb from oxidation is: The oxygen activity for oxidation of Nb, C and P is relevant to the initial [C] content in hot metal. The equilibrium oxygen activity of Nb-O reaction increases with an increase of the [C] content, whereas the equilibrium oxygen activity of C-O and P-O reactions varies oppositely with the [C] content. The reduction ofresults in a decrease of the [C] content required for removing P and retaining Nb, as well as makes the process of dephosphorization more feasible. The increase of temperature decreases the [C] content of selective oxidation of Nb and P, but is unfavorable to dephosphorization.

Thermodynamic Modeling of the Mg-Ni-La-Cu System

The isothermal section at 573 K of the Ni-Cu-La system was experimentally validated as well as the Mg-La-Cu system was thermodynamically evaluated. Four sample alloys in the Ni-Cu-La system were prepared and analyzed by ICP, XRD and BSE/EDS. All the experimental results were compared favorably with the calculated phase relationships. For the Mg-La-Cu ternary system, the isothermal section at 673 K was assessed on the basis of the available results in literatures, which showed a good agreement with the experimental data. Based on the thermodynamic models and parameters of the six binaries and four ternaries, the Mg-Ni-La-Cu system was finally modeled. The non-equilibrium solidification path La0.7Mg0.3Ni2.8-xCux (x=0-0.4) and the vertical section of LaNi5-Mg2Cu were calculated and analyzed from the viewpoint of hydrogen storage alloys design.

Synthesis and Electrical Properties of Mo-ZrO2 Cermet

Under the protected condition of the purified argon atmosphere, Mo-ZrO2 cermets were sintered by Mo powder and ZrO2 powder at 1873K for 2 hours. Mircostructure of cermets were observed by means of XRD, optical microscope and SEM anslysis. Electrical properties of sintered samples with different Mo content and temperature were measured using DC four-electrode method. The results showed that metal phase and ceramic phase were independent of each other. With the reduction of Mo content, Mo metal phase as the continuous network structure is dispersedly distributed in the ceramic phase zone. The electrical conductivity of cermets at room temperature increased with decreaseing of the Mo content. The trend that the high-temperature electrical conductivity of cermets changed with the Mo content is the same as the trend that at the room temperature. When the Mo content is greater than 40%, the high-temperature electrical conductivity increased linearly with increasing temperature. The electrical conductivity of 40mol-% Mo-ZrO2 reached the peak at 1223K and 1473K.

Effects of Mg Addition on Thickness of Galvalume Coating: A First-Principles Study

The presence of Mg addition in bath has been shown to improve the corrosion resistance of the hot-dip Al-Zn alloy coating while adhesion of coating degrades. And the underlying mechanism of the additive effects was not very clear. In this work, first-principles method has been used to investigate the effect of Mg addition on thickness of Galvalume coating. The optimized geometric configurations, total energy and electronic charge distributions for the Mg substitution in Fe2Al5 and FeAl3 phases were obtained. And results indicated that the most favorable sites for Mg substitution in both Fe2Al5 and FeAl3 phases are Al positions. Bonding energy and charge density results show that the addition Mg could not form Mg-Al bond and has little effect on the thickness of alloy layer.

Effect of Water Rinsing Temperature for Steel Substrate on Corrosion Behavior of Hot-Dip Aluminizing Coatings

The relationship between the morphology and protective action of hot-dip aluminizing coatings on Q235 steel have been investigated by SEM, EDS and EIS in 3.5 wt% NaCl aqueous solution. The results indicated that the anti-corrosion performance of the hot-dip aluminizing coatings using steel substrate rinsed by the distilled water at 25 oC was higher than that at 80 oC. The evolution of localized corrosion from pitting to exfoliation corrosion has been found on the aluminum coating surface during immersion, and corresponding equivalent circuit models were proposed to fit the EIS data in the initiation and propagation stages of corrosion process.

Effect of Pulling Velocity on the Unidirectional Solidification Phenomenon of DZ417G Superalloy

In this study, the influence of pulling velocity on temperature field, fluid field and grain structure of a unidirectionally solidified superalloy DZ417G cylindrical casting was investigated by using a 3D cellular automaton finite element (CAFE) model within commercial software CALCOSOFT. The predictions show that temperature distribution in the casting is well in accordance with the experiment result. The solidification front and fluid field are sensitive to changes in pulling velocity. And the pulling velocity should be controlled less than 0.5 mm/s in our experiment so as to effectively decrease the grain number and mean grain deviation.

Effect of Simulation Conditions on Grain Selection during Solidification of Single Crystal Casting

A macro-scale ProCAST and a meso-scale Cellular Automaton Finite Element model (CAFE) are used to simulate the grain selection during solidification with different simulation conditions. To improve the efficiency of the spiral grain selector, the effects of spiral geometries, boundary conditions and nucleation parameters on the grain selection are investigated. Simulation results reveal that the spiral geometries affect the height where the single crystal occurs in the spiral selector when volume nucleation is neglected. The average orientation deviation and grain number is relatively insensitive to volume nucleation and thermal boundary conditions around grain selector, and the thermal boundary conditions in the top of grain selector being of lesser importance.