Metal Additive Manufacturing (AM) is a technology with huge potential in the aerospace, energy and biomedical sectors. However, defects such as pores, cracks and the formation of long textured grains through epitaxial growth prevent further widespread usage. Additional control mechanisms are being developed and one such technique is the use of magnetic fields to modulate the meltpool dynamics and tailor the resulting microstructure.

The AM processes generate large thermal gradients, which lead to the formation of inherent thermoelectric currents. In the presence of an external magnetic field these currents interact to form a Lorentz force that drives fluid flow. This phenomenon, known as thermoelectric magnetohydrodynamics (TEMHD) competes with Marangoni flow, modifying heat and mass transport, leading to changes in the melt pool morphology and a redistribution of solute.

The Lorentz force is the cross product of the thermoelectric currents and the magnetic field, and consequently the behaviour of TEMHD is highly dependent on the orientation of the magnetic field. As an example, for a given orientation of the magnetic field, the Lorentz force, and therefore fluid flow, is directed downward, transporting hot fluid from surface and creating a deep and thin melt pool. In contrast, by reversing the magnetic field, flow goes upward creating a shallow wide melt pool.

We investigate modulation of the melt pool, through a sinusoidal magnetic field, such that the melt pool transitions between these two extremes. The results show that this evolving system has the potential to disrupt the mechanisms that lead to defects, for example, grain competition is highly dependent on thermal conditions, changes with new layers leading to disruption of epitaxial growth.

A bespoke numerical code TESA (ThermoElectric Solidification Algorithm) has been developed to solve this complex problem by intimately coupling solidification, fluid flow and electromagnetism.