Papers by Author: Zhong Ming Ren

Abstract: The problem of free surface deformation is involved in variable fields ranging from material processing to metallurgy. In order to investigate the transient evolution of fluid field and free surface deformation numerically, three numerical simulation methods are proposed among which one is based on level set method, the other two are based on moving mesh method. Afterwards, a benchmark problem of sessile droplet is chosen to test and verify each numerical method. A comparison of each numerical result and experimental result shows a good agreement between each other. Comparison and discussion of three numerical methods are made in the end.

Abstract: The flow state and velocity distribution of liquid metal in the FC-Mold and the influence rules by the magnetic flux density have been investigated when electromagnetic brake adopted, applying mercury as medium to simulate molten steel in the continuous casting process. The velocity measurement has been completed by the Ultrasonic Doppler Velocimeter (UDV) under various magnetic distribution and the influence laws of magnetic flux density on the liquid metal flow in the mold has been analyzed. The experimental results indicate that, when the upper and lower magnetic flux density is 0.18T and 0.5T respectively, a preferable control effect can be obtained, not only the free surface fluctuation can be compressed, but also a plug flow can be rapidly formed.

Abstract: The solidification and process optimization for twin-roll casting of magnesium alloys have been studied. Effects of roll speed, roller diameter, setback length and strip thickness on the position of the solidification front and the surface quality of strip were analyzed through experiments. A kiss-point model which considers the strip thickness, set-back length and roll speed was established to optimize process and enhance the surface quality of magnesium alloy strip. Results showed that the twin-roll casting process could be effectively stabilized and optimized under the direction of the model, and the defectless magnesium alloy strip was obtained.

Abstract: 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.

Abstract: A direct current was imposed during the ageing treatment of cold worked Cu-Cr-Zr alloys. The effect of increasing current density and ageing time on the electrical conductivity and microhardness has been investigated. The electrical conductivity was found to increase by about 22% IACS to a maximum value of 90% IACS. Furthermore, the microhardness increased by 21 HV up to 176 HV. A number of Cr precipitates and Cr-rich clusters were observed after the ageing treatment with direct current. The direct current was found to significantly enhance the efficiency of precipitation which is most probably due to the electron wind force and the electromigration-induced mass transport.

Abstract: The CaZrO3 complex oxide ceramic was synthesized in the development of the potential refractory for melting of titanium alloy, the crucible ( 40XH40mm) was prepared by the solid sintering of mixture of powder (CaO:ZrO2 =1:1) with a small amount of TiO2 as additive at 1750°C. The melting of TiNi and Ti6Al4V was carried out in the inducting furnace under vacuum or/and Ar atmosphere. The interfacial reaction between the melts of alloys and CaZrO3 refractory was investigated by scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDS). It is found that, the thickness of interfacial reaction layer between the ceramic CaZrO3 and the melt of titanium alloys (TiNi and Ti6Al4V) is approximately 30-300 μm, there are few elements such as Ca, Zr, Ti, and Ni diffused through the interfacial reaction layer. These results may provide the basement to designing a novel refractory for melting of titanium alloys.