Study on droplet transfer behavior and porosity defects in narrow-gap laser–arc hybrid welding of titanium alloy

In narrow-gap laser–arc hybrid welding, the droplet transfer behavior indirectly affects the formation of porosity defects by influencing the molten pool disturbance and keyhole stability. To reveal the correspondence between the droplet transfer and porosity under different process conditions, a comparative analysis was conducted on the droplet transfer characteristics and weld porosity distribution with variations in the laser power, wire feeding speed, and welding speed. The results indicate that the droplet transfer mode has a significant correlation with the porosity. Under the parameter combination of a laser power of 3.2 kW, a welding speed of 0.96 m/min, and a wire feeding speed of 9 m/min, the porosity reaches a minimum value of approximately 0.34%. When the laser power increases to 4.2 kW, the droplet transfer transforms into a short-circuiting transfer mode; the welding process fluctuations increase, and the porosity significantly rises. The effect of wire feeding speed on porosity shows a trend of first decreasing and then increasing; when the wire feeding speed is relatively low, the arc stiffness is insufficient, whereas when it is relatively high, the droplet impact is enhanced, and the molten pool disturbance is intensified. When the welding speed deviates from an appropriate range, arc deflection is induced, causing droplets to fall with an offset and altering the local molten pool flow, thereby increasing the porosity.