External Magnetic Field-Assisted Porosity Reduction in Plasma Arc-Based Wire Arc Additive Manufacturing

This study proposed porosity reduction technology for Wire Arc Additive Manufacturing (WAAM) of aluminum alloys that employ a static transversal External Magnetic Field (EMF) to control cathode spot (CS) behavior for the first time, thereby facilitating bubble release, mainly by accelerating the removal of oxide layer. This paper reported effects of EMF strength (Magnetic Flux Density: MFD) on porosity reduction. The pore diameter distributions showed that the number of pores at MFDs of 2 mT and 3 mT decreased to approximately half of that at 0 mT and 1 mT for pore diameters less than 60 μm, indicating that applying EMF with MFD higher than 2 mT especially contributed to reducing the pore formation. The observation presented that the Electrode Negative (EN) arc effectively melted the wire, and the Electrode Positive (EP) arc cleaned the oxide layer on the rear weld pool surface by CSs with EMF. There were two types of bubble release behavior: a weak eruption outside the arc root (Type A), and a strong eruption inside the arc root (or CS) (Type B). Type B is considered to be more effective for porosity reduction, being caused by oxide removal by CS. One possible explanation for this is that the gas bubbles trapped beneath the oxide layer could be strongly drawn out through CS.