Experimental studies and numerical analysis of temperature field and weld bead geometry during laser beam welding of grade 5 titanium sheets

Abstract

Ti-6Al-4 V (grade 5 titanium alloy) is widely applied in critical structures owing to its high strength-to-weight ratio and corrosion resistance; however, its strong reactivity at elevated temperatures complicates fusion welding. Laser beam welding (LBW) was employed in this study using a Nd:YAG laser to produce butt joints. Experimental weld-bead geometry was measured and compared with three-dimensional transient thermal simulations in COMSOL Multiphysics using a conical Gaussian heat source with temperature-dependent material properties. The predicted weld profiles closely matched experimental results, confirming the reliability of the finite element model. Microstructural evaluation revealed acicular α′ martensite in the fusion zone (FZ), resulting in the highest hardness of 383 HV, compared with 332 HV in the heat-affected zone (HAZ) and 297 HV in the base metal (BM). Energy-dispersive X-ray spectroscopy detected only 0.02% nitrogen and 0.23% oxygen in the weld metal, with no measurable hydrogen, indicating effective shielding. X-ray diffraction confirmed that the characteristic α and β phases of the BM were largely retained, with β phase nucleation observed at 70.52° in the FZ, while its absence in the HAZ was attributed to a peak temperature of 1242 K. The welded joints achieved an ultimate tensile strength of 947 MPa, compared to 945 MPa for the BM (~ 100% joint efficiency), and maintained 26.7% elongation, versus 28.1% (~ 95%), demonstrating high strength with only a slight reduction in ductility.