Narrow-gap laser welding with beam wobbling and filler wire and microstructural performance of joints of thick TC4 titanium alloy plates

How to control poor fusion of sidewall and interlayer in narrow-gap laser welding with filler wire of thick plates is an unsolved problem. When the groove width changes in the direction of the plate thickness (for example, V-shaped narrow-gap grooves or preset inverse deformation to offset angular distortion caused by welding), incomplete fusion is more difficult to control, resulting in low yield. Laser welding with beam wobbling and filler wire (LWBWFW) was carried out on narrow-gap butt joints of thick TC4 titanium (Ti) alloy plates with V-shaped grooves. On this basis, the relationship between welding conditions and incomplete fusion under four widths of the groove bottom (4, 6, 8 and 10 mm) was studied. It is found that the key to eliminating incomplete fusion is shown as follows: on the one hand, the beam wobbling amplitude should be appropriate. On the other hand, the ratio of the welding line energy to the wire feed amount should be proper. The former mainly affects incomplete sidewall fusion, while the latter mainly influences incomplete interlayer fusion. Following the above principles, this research obtained well-formed joints of TC4 alloy with the thickness of 30 mm welded by LWBWFW (hereinafter referred to as LWBWFW joints) and the tensile strength of the joints can reach 99.6% that of base metal (BM).