Microstructure and mechanical properties of TC4 titanium alloy laser beam welded joint

The fiber laser welding tests for 3 mm thick TC4 titanium alloy plates are carried out, and the microstructures of the joints are analyzed by the OM and SEM, and the mechanical properties of the joints are described by tensile and hardness tests, and the SEM morphologies of the tensile fracture are observed. The results show that the weld zone is composed of columnar β phase with coarse grains and acicular martensite α', and small secondary α' phases in different directions are formed acicular martensite α'. The microstructure at the boundary between the HAZ and the weld is composed of α' and α phases, the microstructure at the boundary between the HAZ and the base metal is composed of the initial (α and β) and α phases, and the microstructure of the middle transition zone of the HAZ is composed of a small amount of α' and α phase of high temperature β phase ’transformation and initial (α and β) phases. The average tensile strength of TC4 titanium alloy laser beam welded joints is 1 056 MPa, and the average elongation is 9.0%, which are lower than the tensile strength and the elongation of the base metal respectively. The fracture is ductile fracture, and the hardness of the weld zone is the highest and that of the HAZ is the lowest.