Effect of phase transformation and porosity formation on the mechanical behavior of continuous wave Nd: YAG laser beam welded Ti–6Al–4V

Ti–6Al–4V sheets with a thickness of 3 mm were welded using Nd:YAG laser beam welding (LBW). The scanning speed of the laser beam was changed from 3.5 m/min to 6 m/min. The microstructure of the welded region was assessed by various microscopic techniques. The fusion zone geometry exhibited an X shape, and the increase in scanning speed improved the aspect ratio. The heat-affected zone (HAZ) underwent an α′ martensitic phase transformation with a heterogeneous distribution. More ά martensite phase transformation was observed in the fusion zone. Slower scanning speeds produced blocky α phase along with ά martensite. Faster scanning speeds resulted in higher acicular ά martensite. A network of spherical pores was observed. Increased scanning speed reduced pore content. The martensite phase transformation generated a number of dislocations. The weld zone was hardened due to martensite formation. The tensile strength was dictated by both the phase transformation and the porosity content. Faster scanning speed produced joints that matched the base metal strength. The increment in scanning speed changed the fracture mode from brittle to ductile.