Effect of magnetic field frequency on the shape of GMAW welding arc and weld microstructure properties

Aluminum alloy is widely used in aerospace and shipbuilding fields, but it is microstructural and mechanical properties of weld bead are not satisfactory. In this paper, GMAW experiments under the magnetic field were carried out. The effect of magnetic field frequency on GMAW process was analyzed through taking the arc images by high-speed camera, detecting spatter rate, observing metallographic microstructural, testing tensile property and observing fracture SEM appearance. The arc shape and arc movement changed with the variation of external magnetic field frequency, which had a crucial influence on arc temperature gradient and undercooling degree and finally took effect on weld appearance and mechanical properties. The experimental results shown that the arc shape was expanded, arc temperature gradient and undercooling degree decrease, weld bead grain becomes coarse, weld appearance and mechanical properties gets worse below the magnetic field frequency of 60 Hz. The arc shape compressed, arc temperature gradient and undercooling degree increase, weld bead grain becomes refined, weld appearance and mechanical properties gets better over 60 Hz compared with conventional GMAW, the spatter rate reduced by 1.8%, the microstructural grain refined obviously and the tensile strength increased by 31.5 MPa.