Study On Effect Of High Static Magnetic Field On The Solidification Behavior In The Binary Alloy

Metal solidification under high static magnetic field is a new research direction. Thiswork has investigated on the effect of a high magnetic field on the solidification behavior inthe binary alloy experimentally, theory and numerically. The stability of the interface, cell anddendrite during the solidification of signal phase, the eutectic growth, crystal orientation andphase transformation in binary alloy has been studied experimentally and the model is built toanalyze the many kinds of physical effects. Some valuable conclusions have been gained.In the growth of the Al Cu binary single phase alloy, it has been found that an applicationof a high magnetic field has caused the instability and irregularity of the interface, the cell andthe dendrite. Indeed, the field has branched and broken the cell and dendrite. With theincrease of the magnetic field intensity, the primary dendritic spacing increases and the highorder dendritic spacing decreases. Moreover, during the cellular growth under a lowermagnetic field, the ring like structure has formed. The thermoelectric effects on various scalesduring the directional solidification have been found and these effects will induce thethermoelectric magnetic convection (TEMC) in the liquid and the thermoelectric magneticforce (TEMF) on the solid. The irregularity and instability of the interface and the branch andthe irregularity of the cell and dendrite should be attributed to the irregular thermoelectricmagnetic convection (TEMC) in the liquid and the thermoelectric magnetic force (TEMF) onthe solid. Further, the theoretical and numerical models have been built to analyze thethermoelectric magnetic convection (TEMC) in the liquid and the thermoelectric magneticforce (TEMF) on the solid and it has been found that with the increase of the magnetic fieldintensity, the velocity of the TEMC increases and reaches the maximum value in order of 0.1T;and then with the increase of the magnetic field intensity, the value of the TEMC decreases.However, the TEMF imposed on the solid increases lineally with the increase of the magneticfield intensity. Furthermore, a theory of the magnetization and solute buildup in the diffusionboundary layer under a high magnetic field for a binary alloy has been proposed; and the magnetization and solute buildup in the diffusion boundary layer could be partly responsibleto the instability of the planar interface and cell/dendrite. Moreover, in the dendrite growth ofsingle phase in the Al Cu alloy, it has been observed that the <111> crystal direction ofαAldendrite tends to align along the magnetic field. In the dendrite growth of single phase in theAl Ni alloy, it has been observed that the Al3Ni dendrite deflects from the solidificationdirection during the directional solidification under a magnetic field and the lay like structureforms finally under an enough high magnetic field. This should be attributed to themagnetocrystalline anisotropy of theAl3Ni crystal.. In the Al Al2Cu and Al Al3Ni eutectic growth, it has been found that an application of ahigh magnetic field has caused the decrease of the lamellar and fiber eutectic spacing and theformation of the land like structure. Moreover, the high magnetic field has degenerated thegrowth of the lamellar eutectic. Further, a theory of the magnetization and solute buildup inthe diffusion boundary layer during the eutectic growth under a high magnetic field has beenproposed; and the magnetization and solute buildup in the diffusion boundary layer willchange the eutectic spacing and cause the formation of the land like structure. Moreover, anapplication of a high magnetic field is capable of theAl Al2Cu eutectic with the <001> crystaldirection of the eutectic Al2Cu phase. Further, an alignment model of lamellar eutectics undera high magnetic field during directional solidification has been proposed. Moreover, anapplication of the high magnetic field during the eutectic growth will induce thethermoelectric magnetic force (TEMF) on the eutectic lamellae. This force may cause theinstability and the degeneration of the eutectic.Effect of a high magnetic field on the phase transformation has been investigated and amethod to measure the phase transformation temperature in a gradient magnetic field has beenproposed by relating the change of magnetic levitation force to the phase transformation dueto the change in magnetic susceptibility while the transformation occurs. By measuring thetemperature at which the magnetizing force changes abruptly, the phase transformation can bedetected. Through this method, the phase transformation BiMn1.08+L→BiMn in the Mn Bialloy has been investigated and the results has shown that with the increase of magneticfield, the temperature of the phase transformation increased significantly, and in a 10Tmagnetic field the temperature increase was about 20℃. Moreover, it has been found that along with the phase transformation, the high magnetic field has split the BiMn grains in thedirection perpendicular to the magnetic field and split grains further aggregate along themagnetic field direction. Further, a model has been built to analyze the effect of the magneticfield on the phase transformation temperature and it is well consistent with the experimentalresults. Moreover, it has been found that the magnetic field has aligned the MnBi phase withthe <001> crystal direction along the magnetic field direction. Along with the alignment ofthe MnBi phase, the remarkable magnetic anisotropy of the samples has formed; and with theincrease of the time imposed of the magnetic field and the magnetic field intensity, magneticanisotropy of the samples is enhanced.