Laser MIG hybrid welding of Ti-6Al-4V alloy: Leading laser - pulsed arc synergistic regulation strategy and weld forming improvement mechanism

: MIG welding is widely used in industry because of its high efficiency and low cost, but titanium alloy welding often suffers from serpentine beads, discontinuous formation, and severe spatter. Pulsed MIG welding reduces large spatter by rapidly melting the wire during peak current, whereas laser-MIG hybrid welding (LMHW) prevents short circuiting between the molten pool and untransferred droplets. Laser pulsed-MIG hybrid welding (LPMHW) combines these advantages, suppressing cathode-spot drift and spatter while promoting continuous bead formation. LPMHW enabled one-droplet-per-pulse (ODPP) transfer, increasing the droplet-to-pulse ratio from 0.604 for pulsed MIG to 1.0. Electrical signals showed that photoplasma enhanced arc conductivity during the base stage, increasing the average base current and decreasing average base voltage. In the peak stage, the enlarged arc accommodated more photoplasma and metal vapor, raising average peak current and voltage. This accelerated wire melting and stabilized ODPP transfer, thereby improving weld formation. The relatively high cooling rate in the LPMHW fusion zone promoted the formation of abundant acicular α′ martensite, which formed an interlaced basket-weave microstructure. These structures strengthened the fusion zone, giving the LPMHW joint a tensile strength of 995.95 MPa, higher than the base metal. These results clarify the coupling among arc behavior, droplet transfer, weld formation, microstructural characteristics, and mechanical performance in high-speed TC4 titanium alloy welding.