The effect of excitation frequency on novel three-winding magnetic field-assisted MIG welding of 7075 aluminium alloy

A new type of three-winding magnetic field-assisted welding technology is proposed. When the welding speed is 1.2 m / min and there is no magnetic field assistance, the weld shows defects such as pores and cracks, with coarse columnar grains. After applying 80–160 Hz magnetic field, the grains are refined, and the porosity is reduced. However, the 240 Hz high-frequency magnetic field leads to a sharp increase in pore area and a decrease in mechanical properties. The results reveal that the medium- and low-frequency magnetic field drives arc oscillation and molten pool stirring through Lorentz force, promotes pore escape, and refines equiaxed grains.