Effect of transverse magnetic field on arc characteristics and droplet transfer during laser-MIG hybrid welding of Ti-6Al-4 V

In this study, the effect of the transverse magnetic field on the arc characteristics and droplet transfer behavior is investigated during Laser-MIG hybrid welding of Ti-6Al-4 V. Especially, transverse magnetic fields with 0 mT, 8 mT, 16 mT, 24 mT, and 32 mT are studied. Results indicate that an appropriate magnetic field can increase the stability of arc characteristics, improve the droplet detachment efficiency, and reduce the welding defects such as incomplete fusion and undercut. By applying 24-mT transverse magnetic field, the maximum arc area can decrease by 48.7% with its variance changing from 2.81 to 1.06 mm2, indicating that an appropriate transverse magnetic field can shrink the arc and improve its stability. The reason of arc shrinkage is that the electric streamline in the arc rotates away from the laser side to the droplet side due to the influence of external magnetic field. On the other hand, the droplet transfer process becomes more uniform under the appropriate magnetic field. This phenomenon is mainly attributed to the change of Lorentz force direction during droplet rotation, which resultantly increases effective detachment energy. This phenomenon leads to the reduction of the contact time between droplet and molten pool. The droplet transfer form changes from short-circuit transfer to meso-spray transfer under 24-mT magnetic field because of the reduction of the contact time. Therefore, the incomplete fusion and undercut disappears. At last, the appropriated magnetic field parameters during the laser-MIG parameters (2 kW, 160 A, 2 m/min) are concluded as B = 24 mT.