Effect of welding parameters on spatter formation in full-penetration laser welding of titanium alloys

The spatter formation process was observed by high-speed imaging during the full-penetration laser welding (FPLW) process of 4 mm-thick TC4 alloy plates. The effects of process parameters on spatter formation were studied. The results showed that the process parameters have obvious effects on the fluid flow characteristics in the melt pool and the dynamic behaviors of metal vapor in the keyhole, which and then affects the spatter behaviors. When using low-power and low-speed parameters, the fluid flow in the melt pool is unstable. When the melt flow impacts the keyhole, the keyhole opening diameter shrinks instantly, resulting in an immediate increase in the metal vapor eruption velocity at the keyhole opening and leading to the formation of weld spatter with a small size and high flying speed. When using high-power and high-speed parameters, a large amount of metal vapor erupts at high velocity from the keyhole opening transiently, resulting in the formation of a higher liquid column on the keyhole wall. The liquid column fractures to form weld spatter with a large size and low flying speed. When the pressure of the metal vapor in the keyhole is too large, the surface tension of the liquid metal under the keyhole cannot withstand it, causing an explosion on the backside of the melt pool. During the explosion, a large amount of spatter and plasma is ejected from the keyhole exit, and the plasma plume above the melt pool is weakened.