Abstract: Effect of solution treatment temperature on the microstructure and mechanical properties of the laser-deposited Ti-5321 near-β titanium alloy was investigated. The results show that the as-deposited Ti-5321 alloy specimens consist of lath-like primary α phase and β phase, with tensile strength above 1050 MPa and elongation after fracture about 4.5%, and the fracture mode is ductile-brittle mixed fracture. After solution treatment at 770 ℃ and aging, the primary α-phase content decreases, the tip dissolution effect is obvious, the microstructure is mainly composed of short rod-shaped α-phase and precipitates of fine needle-like secondary α-phase, meanwhile the tensile strength of the specimen is above 1180 MPa, the elongation after fracture is about 0.8%, and the fracture mode is changed to brittle fracture. When the solution treatment temperature is 820 ℃ and 870 ℃ respectively, the primary α-phase content is further reduced, the tip dissolution phenomenon is further enhanced, and the primary equiaxed α phase appears, the secondary α phase content increases, meanwhile the tensile strength of the specimen is above 1180 MPa, and there is almost no plasticity. This is because as the solution treatment temperature increases, the size of the secondary α phase decreases, the resistance to plastic deformation becomes stronger, and the strain difference between the secondary α phase and the β matrix increases under external loading, resulting in microcracking and leading to plasticity deterioration.

Key words: Ti-5321 alloy, laser deposition manufacturing, heat treatment, microstructure, properties, fracture mechanism