Improvement of penetration ability of heat source for 316 stainless steel welds produced by alternating magnetic field assisted laser-MIG hybrid welding

Abstract

An alternating magnetic field was designed to increase weld depth of laser-MIG hybrid welded 316 stainless steel joint. The influencing mechanism of alternating magnetic field on improving penetration ability of hybrid heat source of laser-MIG hybrid welding was revealed. The results suggested that the difference of weld depth under different magnetic flux density was attributed to the change of characteristics of arc plasma and laser-induced plasma, droplet transition and keyhole behavior. More compressed arc shape under lower magnetic flux density (LMFD) with 20 m T and 30 m T promoted laser-induced plasma to move along the channel of laser beam, leading to decrease of weld depth. However, the laser-induced plasmas could be dispersed away from the channel of laser beam under higher magnetic flux density (HMFD) of 60 m T and 90 m T, which was the main reason for the increased penetration ability of hybrid heat source. Besides, the droplet transferred to behind the keyhole instead of dropping into the keyhole and more stable keyhole was obtained under HMFD, which were also beneficial for deeper penetration depth of laser energy. Moreover, the motion behavior of charged particles of arc plasma and laser-induced plasma and forces condition of droplet transition were discussed in magnetic field assisted laser-MIG hybrid welding.