Weld morphology, microstructure and mechanical property of laser welded joint of Ti80 alloy

In this paper, we describe experimental laser welding of new-type Ti80 alloy (Ti-6Al-3Nb-2Zr-1Mo) under varying welding speeds. Weld morphology, microstructure and mechanical properties of laser welded joints were carefully investigated using optical microscope (OM), scanning electron microscope (SEM), electron back-scattered diffraction (EBSD) and other methodologies. The results demonstrated that high-quality laser-welded joints were successfully achieved at a welding speed of 40 mm/s, exhibiting a tensile strength of 894 MPa (98% of base metal) and an elongation of 12%. Rapid cooling during the welding process of 40 mm/s promoted the formation of acicular α′ martensite with a volume fraction of 99.5%, refined the grain size to 3.3 μm and increased the hardness to 430 HV. EBSD analysis revealed that dynamic recrystallization (73.5% recovered grains + 23.1% DRX grains) dominated the weld zone (WZ), thus generating 96.2% high-angle boundaries with an average grain size of 3.6 μm. The CDRX mechanism, quantified via kernel average misorientation (0.59°) and GND density (1.66×10 14 /m 2 ), can enhance the strength but restrict the ductility. However, joint strength and elongation at a welding speed of 45 mm/s were reduced to 878 MPa and 5% respectively due to porosity clustering and undercuts. Optimal properties at the welding speed 40 mm/s were mainly attributive to homogeneous α′ distribution and minimal defects (<0.5 vol%). The research results provide the theoretical basis and technical support for the high-quality and efficient welding of titanium alloy components in marine engineering and aerospace field.