Ren Zhongming

Formation of a separated eutectic in Al-Si eutectic alloy

The phenomenon of a “separated eutectic” in Al-Si eutectic alloy unidirectionally solidified with electromagnetic stirring was investigated. It was found that the eutectic silicon could be swept away from the solid/liquid (s/l) interface by the flow, and transferred by the secondary flow to the wall of the crucible, forming a silicon-rich layer on the periphery of the ingot.

Effect of fluid flow on dendritic structure of Al-Si alloy

The effect of fluid flow induced by electromagnetic stirring on dendritic structure of Al-4% Si alloy has been investigated experimentally. It was found that the fluid flow modified the dendritic structure, and along with the increasing velocity of the flow, the dendrite spacing changed from large passing small to large.

STUDY ON THE FLUID FLOW IN SLAB CONTINUOUS CASTING MOLD WITH ELECTROMAGNETIC BRAKE

The flow patterns were simulated by Hg in high speed continuous casting mold with electromagnetic brake.The velocity in mold and fluctuation of meniscus was measured by ultrasonic doppler velocity.The effect of the magnetic field on the fluid flow was analyzed.The influence of magnetic flux density and location on the flow discharged from the nozzle,the velocity in mold,the fluctuation and flow of the meniscus,and the washing intensity of flow were studied.The results showed that the flow discharged from the nozzle was suppressed,the flow in the upper eddy was strengthened, the flow in the lower eddy was weakened,and the fluctuation of free surface and the flow at the meniscus were improved.The magnetic field could not only damp flow,but also change the flow direction and redistribute the flux of liquid steel.When B_(max) was higher than 0.29 T,it was beneficial to optimizing and controling the flow in the mold.

TEXTURE FORMATION AND GRAIN BOUNDARY CHARACTERISTIC OF Al-4.5Cu ALLOYS DIRECTIONALLY SOLIDIFIED UNDER HIGH MAGNETIC FIELD

Directional solidification of Al-4.5Cu alloy refined by adding Al-5Ti-1B has been carried out to investigate the texture formation and grain boundary characteristic of the paramagnetic crystal under a high magnetic field. OM and EBSD were applied to analyze the microstructures solidified at different temperature gradients(G)and magnetic field intensities(B). The results show that at the temperature gradient of 27 K/cm, the orientations of fcc a-Al grains without magnetic field are random. However, as a high magnetic field is imposed, the easy magnetization axes〈310〉of the a-Al grains are aligned parallel to the direction of the magnetic field leading to〈310〉texture. Meanwhile, the ratio of coincidence site lattice(CSL) grain boundaries increases with the increment of magnetic field intensity and reaches its maximum value at 4 T, but decreases as the magnetic field enhances further. On the other hand, when the temperature gradient is elevated, columnar dendrite morphology is exhibited without magnetic field; while a 6 T high magnetic field is introduced, the columnar dendrites are broken and equiaxed grains of random orientations are obtained. The alignment behavior of the free crystals in melt could be attributed to the magnetic crystalline anisotropy of a-Al. Moreover, the influence of fluid flow on the texture formation and CSL grain boundary development under magnetic field is discussed. The absence of convection is benefit for grain reorientation and CSL boundary formation. The application of high static magnetic field will inhibit the macro-scale convection. However, the interaction between thermoelectric current and magnetic field will cause micro-scale fluid flow,i.e., thermoelectric magnetic convection(TEMC). The TEMC will give rise to perturbation near the solid-liquid interface leading to the appearance of freckles as well as the decreasing of the ratio of CSL boundary. Moreover, it is proposed that the formation of CSL boundary is associated with the rotation of the free grains in melt along specific crystallographic axes by magnetic torque.

Influence of 3 T magnetic field on the crystal structure of Zn films prepared by vapor deposition

Zinc films with three different thicknesses in the range of 1—3 μm were deposited on a glass substrate under a high magnetic field of 3 T, and compared with the samples prepared without magnetic field. It’s indicated that the all samples in 3 T magnetic field tend to align in the c-axis direction of zinc crystal and those prepared under in 0 T have lower intensity in c-axis with the thickness increasing, as shown by the X-ray diffraction results. From the scanning electron microscope photographs we found that crystals of zinc films prepared in 3 T magnetic field have refined appearance compared to the ones without magnetic field. Thermodynamic theory was used to analyze the coacervation of zinc aggregates. Preliminary analysis shows that the critical nucleation radius r*M and critical nucleation Gibbs free energy ΔG*M in the magnetic field is less than r* and ΔG* in normal state. Thereby, the nucleation intensity of zinc crystals in 3 T magnetic field is larger than that in 0 T and accordingly the refine ment phenomenon ensues.