Effect of underfill defects on distortion and tensile properties of Ti-2Al-1.5Mn welded joint by pulsed laser beam welding

Abstract

Owing to its more precise control of heat input, pulsed laser beam welding is expected to be a choice for welding thin sheets. In this paper, the Ti-2Al-1.5Mn titanium alloy sheets with a thickness of 0.8 mm were welded by a pulsed Nd:YAG laser beam welding system. The underfill defects, welding distortions, microstructures, and tensile properties of the joints were investigated. The results show that the welding defects are strongly influenced by the welding parameters. The residual distortion is related to the specific heat input. Particularly, the maximum angular distortion increases remarkably for the specific heat input higher than 328.5 J/cm. Further investigations reveal that this is mainly due to the formation of underfill defects, while it is not affecting the maximum residual longitudinal bending distortion. In forming underfill defects and changing acicular α′ phase morphology in the fusion zone (FZ) of the welded joint, 328.5 J/cm is a critical specific heat input. Furthermore, tensile test results reveal that the fracture positions are closely related to the underfill rate.