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The intermittent electromagnetic fields with a large ∂B/∂t can enhance the properties of ferromagnetic materials and significantly affect paramagnetic materials. In this study, the effect of a pulsed electromagnetic field on the crystal orientation of the primary phase and microstructure evolution of an Al-Zn-Mg-Cu alloy was investigated. A mathematical model was developed to describe crystal rotation under a pulsed electromagnetic field. The model predictions show that the magnetic energy difference generated by the magnetic anisotropy of the primary crystal produces primary phases with sizes of 225-100 μm to rotate into a <111> preferred orientation. The lattice constant, the interplanar spacing, and the microstrain increase with the duty cycle of the pulsed magnetic field, especially for the (111) and (200) crystal planes. This study provides preliminary theoretical support for using pulsed electromagnetic fields to control the orientation and microscopic properties of materials. Some organic and inorganic materials exhibit unusual phenomena under electromagnetic fields. Grain rotation, deformation, and orientation changes are generated in metallic materials during electromagnetic solidification processing, and levitation and structural transformations are observed for nonferromagnetic materials. Thus, the magnetic force is considered to be the main factor in materials processing. The magnetic force has two components. The parallel component causes a magnet pulls ferromagnetic and paramagnetic materials and repels diamagnetic materials. The rotational component results in the generation of a Lorentz force from the interaction of the current and the external magnetic field. The parallel magnetic force is mainly used for magnetic separation, magnetic levitation 1 , and to measure the magnetic susceptibility 2. The magnetocrystalline anisotropy of materials determines the magnetic susceptibilities in different crystal planes. Thus, the rotational magnetic force can be used to construct materials with ideal crystal orientations and texture distributions 3-8. The magnetic anisotropy is widely used to control crystal orientation, for example, to realize magnetic directional alignments of an undoped Cu-O superconducting magnet and Zn film are achieved. For the FCC (face-centered-cubic) crystal, when the magnetic susceptibility along the direction parallel to the c-axis of the unit crystal (χ c) is higher than that perpendicular to the c-axis (χ ab), the unit crystal grows along the c-axis, which is parallel to the external field, H 9-11. Magnetic anisotropy in ion-doped materials results from single-ion anisotropy in the magnetic field 12. Recently, Liu et al. 13 investigated the influence of a magnetic field on the crystal orientation and magnetic properties of Fe-4.5 wt% Si. The crystal orientation of the Fe-4.5 wt% Si alloy was rotated into the <100> axis, and strong Goss texture was obtained under a 6-T high static magnetic field. Zhong et al. 14 found that an Al-4.5 Cu free crystal rotated in the melt state to a...

In this paper, a transient numerical simulation method was used to analyze the direct chill casting process of 7A04 alloy under electromagnetic pulse treatment. The distribution and evolution of the electromagnetic force, fluid and thermal fields were studied to determine their effect on the solidification characteristics of alloy ingots. A modified nucleation theory for the refinement of grain size was presented considering the effect of electromagnetic energy on the critical Gibbs free energy $\Delta {G^*}$ of the unity, which was verified by the corresponding experiments. The results showed that the swirl rings of the axial section in the melt were restrained and a lower temperature gradient was formed in the radial section when the magnetic flux intensity was increased. Under these conditions for nucleation, the grain refinement could be explained by the electromagnetic pulse energy that reduced the energy barrier and improved the nucleation rate, either heterogeneous nucleation or homogeneous nucleation.

Al-Si-Mg-Cu-Ni alloy is widely used in the manufacture of high-performance car engine parts. Coarse, dendritic α-Al and large primary Si are common in Al-Si-Mg-Cu-Ni alloy DC casting billet, which is harmful to the performance of the final product. In this paper, a pulsed magnetic field melt treatment technique was applied to the melt in the launder of a DC casting platform to modify the α-Al and primary Si in the billet. A transient numerical model was established to analyze the electromagnetic field, flow field and temperature field in the melt during the pulsed magnetic field treatment. The effect of the magnetic energy on the clusters in the melt was analyzed. We found that during the pulsed magnetic field melt treatment, the number of clusters close to the critical size was increased due to the cluster formation work being reduced by the magnetic energy, which facilitated nucleation and refined the solidification structure. Furthermore, the flow velocity increased, and temperature homogenized in the melt during the pulsed magnetic field melt treatment, which benefitted the clusters close to the critical size distributed and maintained in the melt uniformly. The experimental results show that the α-Al and primary Si were small and homogeneous following the pulsed magnetic field melt treatment. The size of α-Al and primary Si was reduced by 25.6–44.4% and 32.2–54.1%, respectively, in the billet center compared to the conventional process.

3(a), in addition, a low internal dislocation density was revealed, which resulted from the great reduction of single rolling pass during continuous rolling, these internal dislocation and deformation band provide nucleation site, and result in the high nucleation rate of ferrite crystal. Moreover, the dislocation/precipitation interaction in ferrite matrix would be one of the dominant reasons of strengthening.8) It was observed that the precipitates are mostly spherical in appearance, and the TEM microstructure of extraction replica also reveal the existence of precipitates clearly in Fig. 3(b). Large precipitates have been identified as carbide particles through electron dispersive analysis as shown in Fig. 3(c), but the size distribution of other shapes could not be estimated because the number was so small, which indicates that they are present in the austenite prior to precipitate from the austenite during cooling.Selective area electron diffraction study was carried out with TEM to clarify the orientation relationship between the tiny precipitates and the a-Fe matrix. beam parallel to [100] direction. A lot of diffraction spots are seen in addition to the matrix spots. It is difficult to determine the relationship between the particles and the matrix from this pattern. If we assume that the particles have a cube relationship with the matrix, the spots that do not belong to the matrix correspond very well to those of ferrite phase with the zone axis being parallel to [001]. Thus, the assumption that the tiny have cube-cube relationship with the matrix is reasonable. The dark field image in Fig. 3(e) is taken using the super lattice spots shown in the inset diffraction pattern of Fig. 3(d) and reveals that the precipitates (bright) are very small and coherent with the matrix; it would show a very effective pinning in ferrite matrix.9) The coherent orientation relationship between the tiny precipitates and the a-Fe suggests that these tiny particles may precipitate from the a-Fe instead of the g-Fe. Furthermore, the coherent orientation relationship may influence the interfacial energy between the particle and the matrix as well as the nucleation process of the particles. 10)As shown in Fig. 4(a), a small cluster of particles were observed at junctions of a curved grain boundary. The recrystallization nuclei in these alloys would form primarily adjacent to nanometer-sized particles that are produced during casting and the movement of the boundary need overcoming the pinning force of particle, which will result in a local increase in the driving force due to changes in boundary curvature and thermal activation.11) In conclusion, small particles can restrict subsequent grain boundary movement and promote a fine-grained microstructure through Zener drag. Smith 12) attributes to Zener the analysis of the pinning force exerted by particles on grain boundary, and Azmir Har et al. had also simulated particle pinning force acting on the grain boundary.13) The geometry of such an interaction is shown in Fig. 4(b).C...