Zhong Yunbo

EFFECT OF STATIC MAGNETIC FIELD ON THE MORPHOLOGY AND Si CONTENT OF Fe-Si COMPOSITE COATING

The Si particles with average size of 2 μm were dispersed in plating solution,and the electrodeposition process of Fe-Si composite coating under a static magnetic field was studied.The influences of orientation,flux density of magnetic field(MFD) and current density on the morphology and Si content of Fe-Si composite coatings were discussed.It was found that the Si content of coatings for vertical electrodes increased significantly with increasing the MFD in both parallel and perpendicular magnetic field(regard to current) with the MFD ranging from 0 T to 1 T.In the case of aclinic electrodes,the Si content of coating can reach 37.94%(mass fraction) without magnetic field.However,after applying a perpendicular magnetic field,the Si content of coatings decreased sharply with increasing the MFD(only 2.83%at 1 T).Meanwhile,many striated iron matrix protuberances with Si particles appeared perpendicular to the direction of magnetic field on the coatings surface.Moreover,the Si content of coatings decreased with increasing current density for both aclinic and vertical electrodes in 1 T perpendicular magnetic field,while that for vertical electrodes first increased and then decreased and reached maximum value at about 20 mA/cm~2 in 1T parallel magnetic field.Theoretical analysis shows that the change of morphology and Si content of coatings were mainly attributed to the formations of macroscopic magnetohydrodynamics(MHD) and micro-zone MHD effect caused by Lorenz force.

Effect of distribution of magnetic flux density on purifying liquid metal by travelling magnetic field

The distribution of the magnetic flux density in the magnetic field generator which provided travelling magnetic field was determined. The experiments using liquid gallium and aluminum — silicon alloy to observe the turbulent flow or remove inclusions were performed to obtain the basic principles how the distribution of the magnetic flux density took effect on removing inclusions from molten metal by electromagnetic field. The suitable area in the field for purifying metal was suggested.

Crystalline and Magnetic Enhancement of Nanocrystalline MnZn Ferrites Fabricated under a High Magnetic Field

Nanocrystalline Mn0.6Zn0.4Fe2O4 particles are synthesized under magnetic fields of 0 and 6 T, and their structural and magnetic properties are investigated. The magnetic field enhances the grain size and the lattice strain. Magnetic measurements show that the majority of the 6 T nanoparticles are superparamagnetic nearly from 40 to 300 K. It is interesting that the saturation magnetization of the 6 T sample is about 18% and 16% higher than that of the 0 T sample at 120 and 300 K, respectively.

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.

Phase Growth in Fe-Fe50wt%Si Diffusion Couple Under a Magnetic Field

Intermediate phases and their thickness in Fe-Fe50wt%Si diffusion couples were studied. Diffusion couples were annealed at 1050°C and 1150°C with / without magnetic field. Microstructures of diffusion couples were analyzed using scanning electron microscopy (SEM), electron backscatter diffraction (BSE) and energy dispersive spectroscopy (EDS). From the results, we know that two silicide phases (Fe2Si, Fe3Si) were only found after short-time heating whether the samples were treated with or without magnetic field. Silicide phases of Fe2Si and Fe3Si disappeared when samples heated for longer time. Meanwhile, the thickness of FeSi layer heated under magnetic field was smaller than those without magnetic field at the same temperature and diffusion time, and the growth of FeSi phase obeys the parabolic rate law.