Review of the Effect of Different Magnetic Field on Metal Solidification

Alloys prepared in a magnetic field environment have excellent comprehensive properties and are widely used in industrial production, transportation, aerospace, and other fields. The hardness, wear resistance, and other service properties of the alloy vary with the magnetic field parameters. Therefore, summarizing the mechanisms of different magnetic fields in the metal solidification process is of great significance for developing auxiliary metal technology. This paper summarizes the studies and exploration of metal surface processing by many researchers in different magnetic field environments. In addition, this study explores the rules of nucleation and growth of metal materials under the assistance of magnetic fields. According to the aspects of the microscopic morphology of the grains and the macroscopic properties of the alloy, the changes in heat and mass transmission, crystal boundary shape variation, increase in nucleation rate, and grain size refinement are analyzed, and the effects of the steady, pulsed, and alternating magnetic fields on metal solidification are revealed. The various influences of different magnetic fields are discussed in this paper, such as magnetic induction, intensity produced by the magnetic field, and charged particles within the melt by the Lorentz force. In the process of metal solidification assisted by a steady magnetic field, both the thermoelectric force generated by the thermoelectric current and magnetic field and the electromagnetic brake force generated by the natural flow of the melt jointly affects the dendrite growth and internal flow of the melt, which is essentially the Lorentz force under the action of a magnetic field. Furthermore, the magnetic induction intensity is the most crucial factor affecting the electromagnetic brake and thermoelectric forces. The combined effect on the melt first increases and then decreases with increasing magnetic induction intensity. Pulsed magnetic fields are essential in improving the magnetism, corrosion resistance, and electrochemical performance of molten metals through wall ionization, electromagnetic oscillation, and the Joule thermal effect. The various effects of the magnetic field are concentrated in the internal flow enhancement and temperature gradient reduction of the molten pool. Electromagnetic stirring and forced convection promote dendrite breaking and grain refinement under an alternating magnetic field. Furthermore, the phase distribution is more uniform and inhibits compositional segregation. The application of metal solidification in a magnetic field environment focuses on emerging surface processing technologies such as deposition and cladding from traditional alloy manufacturing processes such as casting and welding. The exploration of new processes in a magnetic field environment, such as magnetic-field-assisted coating solidification, is also the future development direction of this field. The research method has changed from a simple performance enhancement effect test to a theoretical model calculation. In conclusion, grain refinement and alloy performance improvement are comprehensive embodiments of heat and mass transmission and the magnetic force in the molten pool under the action of a magnetic field. The mechanism of action of the metal solidification process under different magnetic fields gradually tends to be consistent. Refining and quantifying the various effects of different magnetic fields on the alloy solidification structure, unifying grain change processes and mechanisms, and other studies still require scholars' unremitting efforts. A comprehensive study and comparison of the steady, pulsed, and alternating magnetic fields on metal solidification characteristics and mechanisms are summarized, which helps unify the debate on the metal solidification mechanism in a magnetic field environment, fills in the gaps in metal surface processing technology in a magnetic field environment, and has reference significance for promoting research on high-performance metal surface preparation.