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To evaluate the metallurgical effect of mold electromagnetic stirring (EMS), the large eddy simulation (LES) model coupled with discrete phase model was developed to investigate the transient fluid flow, solidification, and inclusion transport in a vertical-bending slab continuous caster under mold EMS. Both the accuracy of predicted magnetic flux density and shell thickness were validated by comparison with the measured data. The results show that the flow field is transiently asymmetric without EMS, the variation of temperature field, solidified shell thickness, and inclusion distribution within the solidified shell are closely related to the flow pattern. Most of inclusions would aggregate at the mold inner radius owing to the buoyancy. The application of EMS can improve transient asymmetry of flow pattern within the mold through controlling the horizonal flow, which can further homogenize temperature and solidified shell thickness, increase removal rate of inclusions, and improve the uniformity of inclusion distribution within the slab. Meanwhile, EMS can also benefit to the cleanliness of subsurface due to its washing effect. Finally, the industrial application also verified the superiority of EMS, in which the area fraction of large size inclusions decreases to 3.2 ppm under the EMS current of 600 A. [ABSTRACT FROM AUTHOR]

A new two-way coupled magnetohydrodynamic (MHD) model considering the dynamics change of electromagnetic force at steel–slag interface was established to investigate the multiphase flow and slag entrapment in slab continuous casting under mold electromagnetic stirring (EMS). The transient turbulent flow and the steel–slag interface behavior were described by solving the large eddy simulation (LES) model and volume of fluid (VOF) model. The level fluctuation, the location, and net mass of slag entrapment were quantitatively evaluated. By comparing the predicted level height within the in-situ measurement, the results show that the two-way coupled MHD model can better reveal the multiphase flow under EMS. The type of slag entrapment is closely related to the flow pattern, the vortex formation is predominant under the lower EMS current, while it changes to the shear-layer instability under the relatively high EMS current, the proportion of vortex formation slag entrapment decreases to 30.7 pct under the EMS current is 600 A. The tendency of net slag entrapment rate is the same as that of level fluctuation, with the increase of EMS current and casting speed, both the level height and net slag entrapment rate decrease firstly and then increase. Therefore, it is necessary to match the casting speed and EMS current to avoid the slag entrapment in actual production. The net slag entrapment rate is 0.034 kg/s, under the condition of 1.2 m/min casting speed and 600 A EMS current. [ABSTRACT FROM AUTHOR]

The effect of the direct current (DC) on the solidification structure in the directional solidification of Al–15Sn–1Cu alloy under 10 T magnetic field was investigated experimentally and numerically. The experimental results show that coarse columnar grains are observed when no DC is applied. However, the microstructure transforms from columnar dendrites to irregular dendrites, and the columnar-to-equiaxed transition (CET) occurs with the application of DC. The numerical results show that the Lorentz force acting on the dendrites can be increased by the application of DC. Additionally, the torque created by the Lorentz force results in the stress concentration at the roots of dendrites arms. The stress increases with the DC when it is larger than the thermoelectric current. Consequently, the dendrites break into fragments when the stress exceeds a certain value and CET occurs. The results indicate that the application of DC facilitates CET at higher withdrawal speeds. Furthermore, this work may initiate a novel method for CET via applying the DC in directional solidification under 10 T magnetic field. [ABSTRACT FROM AUTHOR]

Convection-driven solute transport has an important effect on the evolution of dendrites during solidification. A unified magnetic field-phase field-lattice Boltzmann model is developed to investigate dendrite growth under a transverse magnetic field (TMF). The accuracy of the numerical model is validated by thermoelectric current calculation and experimental dendritic morphology. Results show that the TMF application changes the dendrite morphology from symmetry to tilt, and makes the flat solidification front become steep. The dendrite tilt is due to the different solute distributions on both sides of the tip. The solute distribution difference is caused by the existence of ring-like flow driven by thermoelectric magnetic convection (TEMC) around the dendrite tip. With the increase of magnetic field intensity, the tilt angle of the dendrite array varies nonmonotonically. As a comparison, with the increase of temperature gradient, the tilt angle increases monotonically. The variation difference of the tilt angle is the result of the competition between TEMC and magnetic damping convection, which are induced by Lorentz forces from different sources. [ABSTRACT FROM AUTHOR]

Suppressing the melt convection in the solidifying ingot is still considered to be a challenging task. By applying a high-magnetic field (HMF), we achieved a diffusive condition for the crystal growth. The atomic interdiffusion coefficient in the Al–Cu melt was measured in the HMF to define the critical magnetic flux density (MFD) for the diffusive crystal growth in the melt. A diffusive growth state was achieved in the melt when the MFD was greater than a critical 2.9 T. The influence of HMF on crystal growth was investigated by X-ray computed tomography. The HMF increased the size of crystal, but it decreased the crystal number and the curvature of dendrite tips as well as the specific surface area of dendrite. A transition of dendritic arms from seaweed to dendrite was observed after applying an HMF. Interface shape distribution maps showed that the HMF increased the proportion of ellipsoid shapes and decreased the proportion of hyperbolic shapes of solid–liquid interface. These were attributed to the decrease of constitutional supercooling caused by the magnetohydrodynamic effect. This work provides a new path to obtain a diffusive condition for crystal growth. [ABSTRACT FROM AUTHOR]

Magnetic-controlled Electroslag Remelting (MC-ESR) process has been proposed to improve the inclusion removal efficiency in recent years. In this study, the effects of axial static magnetic field (ASMF) on liquid melting film (LMF) and inclusion removal during this period in ESR process of GCr15 steel were studied by a series of MC-ESR experiments. The thickness of the characteristic position of LMF was reduced by 18.6 to 90.3 pct when a 50 mT ASMF was applied. The number and size of the inclusions in LMF were also decreased. In addition, the mechanisms of LMF thinning and inclusion removal efficiency improvement enhanced by the ASMF were interpreted in detail. Furthermore, a numerical simulation of the inclusion migration in LMF was also carried out to support the proposed mechanisms to some extent. [ABSTRACT FROM AUTHOR]

The present study investigates the evolution of the micro- and macrostructure and tensile property of the Cu-15Ni-8Sn (weight percent) alloy prepared by horizontal continuous casting and electromagnetic stirring (EMS). The results show that the application of EMS is beneficial for grain refinement and for microstructure transformation from the dendrite to the rosette structure and that it leads to a significant improvement in the tensile property. The forced flow induced by EMS homogenizes the temperature field ahead of the solid-liquid interface, disturbing the heat flow direction and resulting in the columnar to equiaxed transition. The grain refinement under different electromagnetic stirring frequencies is mainly derived from the homogenization of the temperature and the remelting of dendritic arms. In addition, the evolution of the tensile property with and without EMS is discussed from the perspective of fracture mode and fine-grain strengthening. [ABSTRACT FROM AUTHOR]

A transient three-dimensional coupled numerical model has been established to clarify the influence of the external transverse static magnetic field (TSMF) on droplet evolution behaviors during the electroslag remelting (ESR) process with an alternating current (50 Hz). The development of the electromagnetic field code and the calculation procedure showed that the periodic inverse Lorentz force (50 Hz) could be fully coupled with the volume of fluid model in each iteration when an external TSMF of 0.05 T is superimposed. The droplet evolution behaviors with and without the external TSMF were demonstrated and analyzed. The numerical results showed that the huge periodic inverse Lorentz force could smash the droplet neck into numerous smaller droplets during the ESR process with the external TSMF; simultaneously, the interfacial area and falling time could be increased, indicating that the purification efficiency could be expected to improve. [ABSTRACT FROM AUTHOR]

An external direct current (DC) was introduced to counteract the thermoelectric magnetic effect during the directional solidification of Sn-10 wt pct Bi alloy under a 0.5 T transverse static magnetic field. The results show that the single-side Bi segregation induced by the thermoelectric magnetic effect gradually becomes weakened, disappeared, and then reversed with the increasing current density of the external DC. Therefore, a new method for counteracting the thermoelectric magnetic effect during materials processing under the magnetic field was proposed. In order to verify this method, the absolute thermoelectric power of Sn-10 wt pct Bi alloy and the internal thermoelectric current under the experimental conditions were measured and calculated, respectively. A 2D numerical simulation was established to simulate the evolution of the solid-liquid interface morphology, flow field, and composition segregation with the increasing current density of the external DC during directional solidification under a transverse static magnetic field. The present study not only facilitates the understanding of the effects of the forced flows on the directionally solidified microstructures and composition segregation, but also provides a new way for eliminating segregation and obtaining the higher-quality solidification structure by using the electromagnetic compounding technique. [ABSTRACT FROM AUTHOR]

In situ solidification experiments on Zn-6 wt pct Bi immiscible alloys were conducted to investigate the droplet evolution under high static magnetic fields (HSMFs). The results showed that a microstructure with extremely fine Bi-rich particles distributed in the matrix can be obtained under an HSMF of 29 T. The average diameter of the Bi-rich phase decreased with the increasing magnetic flux density. Stokes sedimentation disappeared when the HSMF was larger than 18 T. Starting at an HSMF of 18 T, Bi-rich droplets grew via pure diffusion in the liquid matrix. The HSMF decreased the spacing of the droplet arrays when the cooling rate (R) was approximately 1600 °C/min. The formation of a Zn-rich phase surrounded by a Bi-rich shell at HSMFs below 18 T, when R was approximately 60 °C/min, was attributed to the thermoelectric magnetic force. [ABSTRACT FROM AUTHOR]

High magnetic fields are widely used to improve the microstructure and properties of materials during the solidification process. During the preparation of single-crystal turbine blades, the microstructure of the superalloy is the main factor that determines its mechanical properties. In this work, the effects of a high magnetic field on the microstructure of Ni-based single-crystal superalloys PWA1483 and CMSX-4 during directional solidification were investigated experimentally. The results showed that the magnetic field modified the primary dendrite arm spacing, γ′ phase size, and microsegregation of the superalloys. In addition, the size and volume fractions of γ/ γ′ eutectic and the microporosity were decreased in a high magnetic field. Analysis of variance (ANOVA) results showed that the effect of a high magnetic field on the microstructure during directional solidification was significant ( p < 0.05). Based on both experimental results and theoretical analysis, the modification of microstructure was attributed to thermoelectric magnetic convection occurring in the interdendritic regions under a high magnetic field. The present work provides a new method to optimize the microstructure of Ni-based single-crystal superalloy blades by applying a high magnetic field. [ABSTRACT FROM AUTHOR]

The electromagnetic vibration (EMV) generated by the action of the AC current and the magnetic field was applied in the crystallizer during the semi-continuous casting of the Al-15 wt pct Sn alloy. The influences of the electromagnetic vibration frequency (EMVF) on the metallographic structure, inverse segregation, and tensile properties were studied. The results indicated that the equiaxed grain ratios of the slabs were increased by decreasing the EMVFs from 500 to 5 Hz. The inverse segregation around the sides of the slab was improved at a low EMVF. The results of the 3D numerical simulation showed that the forced flows led to the refinement of grains and the improvement of the inverse segregation. The slabs with equiaxed grains which were produced with the low EMVFs showed the poor tensile properties comparing to the slabs with columnar grains obtained with the EMVFs of 50, 200, and 500 Hz and without the EMV. This phenomenon was mainly due to the distribution of the brittle Sn-rich phases: the reticular Sn-rich phases appeared around the boundary of the equiaxed grains, while the worm-like Sn-rich phases appeared between the column dendrites intermittently in the slabs with columnar grains. [ABSTRACT FROM AUTHOR]

A transparent physical model was set up to investigate the influence of the remelting current frequencies on droplet evolution during the magnetic-field-controlled electroslag remelting process. Physical simulation experiments were done under the remelting current of 8 A with frequencies ranging from 10 to 500 Hz, and a transverse static magnetic field (TSMF) of 0.7 T was superimposed simultaneously. The high-speed camera was used to record the evolution behavior of the droplet. Representative processes of formation and detachment of the droplets were observed under different conditions. The results showed that there was little influence of the current frequencies on the evolution behavior of the droplet without the external magnetic field. Nevertheless, if a TSMF was introduced, the liquid droplet's neck would be smashed into a lot of smaller droplets when the remelting current frequencies were lower than 100 Hz, while the smashing effect disappeared when the frequencies were higher than 100 Hz. The mechanism of the smashing effect was discussed. Statistical work was done to obtain the quantitative data to give a clear result revealing the influence of the remelting current frequencies on droplet evolution. The decrease in the diameter of the liquid droplets would remarkably increase the interface area and shorten the migrating distance of the inclusions in the droplets, which meant that a higher purifying efficiency could be expected. [ABSTRACT FROM AUTHOR]

Realizing improved strength-ductility synergy in eutectic alloys acting as in situ composite materials remains a challenge in conventional eutectic systems, which is why eutectic high-entropy alloys (EHEAs), a newly-emerging multi-principal-element eutectic category, may offer wider in situ composite possibilities. Here, we use an AlCoCrFeNi2.1 EHEA to engineer an ultrafine-grained duplex microstructure that deliberately inherits its composite lamellar nature by tailored thermo-mechanical processing to achieve property combinations which are not accessible to previously-reported reinforcement methodologies. The as-prepared samples exhibit hierarchically-structural heterogeneity due to phase decomposition, and the improved mechanical response during deformation is attributed to both a two-hierarchical constraint effect and a self-generated microcrack-arresting mechanism. This work provides a pathway for strengthening eutectic alloys and widens the design toolbox for high-performance materials based upon EHEAs. Producing in situ composite materials with superior strength and ductility has long been a challenge. Here, the authors use lamellar microstructure inherited from casting, rolling, and annealing to produce an ultrafine duplex eutectic high entropy alloy with outstanding properties. [ABSTRACT FROM AUTHOR]