The effect of laser welding process parameters on the mechanical and microstructural properties of V–4Cr–4Ti structural materials

This paper reports a systematic study which examined the use of a pulsed Nd:YAG laser to weld sheet materials of V–Cr–Ti alloys and to characterize the microstructural and mechanical properties of the resulting joints. Deep penetration, defect-free, and oxygen contamination free welds were achieved under an optimum combination of laser parameters including focal length of lens, pulse energy, pulse repetition rate, beam travel speed, and an innovative shielding gas arrangement. The key for defect-free welds was found to be the stabilization of the keyhole and providing an escape path for the gas trapped in the molten weld pool. Oxygen and nitrogen uptakes were reduced to levels only a few ppm higher than the starting material by design and development of an environmental control box (ECB). Laser-applied post-weld heat treatments showed that five-passes of a diffuse laser beam over the welded region softened the weld material, especially in the root region.