Effect of Combined Direct Current Electric Field and Pulsed Magnetic Field on the Transient Melt Pool in Laser Additive Manufacturing Process

The application of a pulsed magnetic field (PMF) during a metallurgy solidification process has proven to be an effective method in refining the grain size and improving the mechanical performance of the material. However, fewer works were reported in the realm of laser additive manufacturing (LAM) and the mechanism of grain refinement consequent to the PMF is still unclear. In this work, numerical models were developed to study the thermal-fluid characteristics in the Ti-alloy melt pool generated during the laser scanning process under the effect of a combined direct current (DC) electric field and PMF. The temperature field and magneto-oscillation effect in the melt pool were discussed to elucidate the resultant microstructure evolution. The results show that the application of a combined DC electric field and PMF could decrease the maximum temperature in the melt pool, but increase the temperature gradient at the liquid-solid interface. The electric-magnetic field can lead to a notable increase in the magnitude of the fluid velocity and a greater fluctuation in the magnitude. A more refined microstructure is expected to be obtained, of which the mechanism may be ascribed to not only the increased temperature gradient, solidification growth rate, and cooling rate at the liquid-solid interface but also the enhanced fluid convection and continuous impulse force in the melt. For better grain refinement, the preferable duty cycles of the PMF should be <50%. The findings of this study may give a new insight into the electromagnetic controlling methods for LAM of Ti-alloy parts.