Abstract
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.
Highlights
Titanium alloys have been used in the aerospace, electronic communication, precision instrument, petrochemical industry due to its low density, high specific strength, good ductility, and excellent high-temperature mechanical properties[1, 2]
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
The studies in recent years indicated that the stability of the welding process and the welding bead appearance is influenced by arc performance[8] and droplet transfer[9]
Summary
Titanium alloys have been used in the aerospace, electronic communication, precision instrument, petrochemical industry due to its low density, high specific strength, good ductility, and excellent high-temperature mechanical properties[1, 2]. Considering the above studies, it is confirmed that the arc performance and metal transfer behavior has a significant impact on the microstructure properties, welding penetration depth, welding bead appearance. Zhang et al.[23] shows that the external longitudinal magnetic field (16 mT) can increase the the stability of welding arc and affect the force on droplet transfer in the laser-MIG hybrid welding of 316L. There are few systematic studies on arc performance and metal transfer in transverse magnetic field-assisted Laser-MIG hybrid welding of Ti-6Al-4V Titanium alloy. This work studies the influence of the external magnetic field on the arc performance and droplet transfer in laser-MIG hybrid welding for Ti-6Al-4V, which can provide further guidance to improve the welding stability and weld quality. In order to protect the welding joint from oxidation, the pure argon with the flow rate of 2 m3/h is provided as the shielding atmosphere
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