Influence of alternating magnetic field on microstructure and mechanical properties of laser-MIG hybrid welded HG785D steel joint

Abstract

The work aimed to investigate the effects of alternating magnetic field on the microstructure, mechanical properties and plasma characteristics during laser-MIG hybrid welding of HG785D steel. The weld appearance was improved and the weld depth was significantly enhanced by an alternating magnetic field. The same microstructure type of lath martensite (LM) was obtained in the arc zone and laser zone of all hybrid welded joints. However, grains in the arc zone were significantly refined and the ratio of high-misorientation angles was increased under alternating magnetic field. The average grain size in the arc zone reduced from 4.60 to 3.67μm with a magnetic flux density of 30 mT. The average microhardness of the arc part and the laser part increased from 356 and 378 to 388 and 393HV, respectively. The grain refinement and increased ratio of high-misorientation angles led to an improvement in low-temperature impact toughness. The low-temperature impact toughness was 184J with a magnetic flux density of 30mT, which was 95.7% higher than that without the alternating magnetic field. Additionally, the shielding effect of the hybrid plasma was suppressed with the magnetic flux density of 10–30mT, leading to an increase in the penetration ability of hybrid heat sources and weld depth. However, the penetration ability of the hybrid heat source was no longer enhanced with a further increase in magnetic flux density.