Improving spreadability of molten metal in MIG welding-brazing of aluminum to steel by external magnetic field

Abstract

A modified metal inert gas (MIG) welding-brazing process of aluminum and steel with the assistance of external magnetic field (EMF) was proposed in this study. An alternative EMF along the welding direction was used to promote the arc and the droplet to swing along the weld width direction by producing an alternative electromagnetic force perpendicular to the welding direction. The effect of the excitation current level and frequency on weld bead appearance, spreadability of molten metal and the welding process stability was investigated by experimental observation. As the excitation current level increased, the width of the weld seam was increased and the spreadability of the molten metal was enhanced. When it was beyond a critical level, the arc stability was disrupted. Excessive excitation current caused the excessive inclination of the arc especially in base current stage, which was extremely easy to result in arc extinguishing. When the frequency of the excitation current changed from 2 Hz to 15 Hz, the weld width was decreased. If the excitation current exceeded 15 Hz, the weld width kept constant. The wetting angle of the aluminum metal was decreased as the optimized EMF was applied. Besides, the tensile strength of the joint was enhanced due to the enhancement of spreading of molten metal under the action of EMF.