Abstract: Ti-6Al-4V titanium alloy specimens formed by L-PBF (laser powder bed fusion) were heat treated at different temperatures, the microstructure and mechanical properties of which were observed and tested by means of optical microscope, scanning electron microscope, tensile testing machine and impact testing machine. The results show that at 600-800 ℃, with the increase of temperature, the fine acicular α′ martensite is decomposed into α+β phase, and the microstructure shows a similar hierarchical structure to the sedimentary specimens, interleaving each other and showing more orientations. When heat treated at 800 ℃, the specimens obtain excellent comprehensive mechanical properties, with the tensile strength up to 1019 MPa, elongation of 14.5% and impact absorbed energy up to 49 J, which can be used as the conventional heat treatment process for the Ti-6Al-4V titanium alloys formed by L-PBF. After heat treatment at the temperature above 1000 ℃, the primary β columnar grains gradually disappear, and the equiaxed β grains appear, and the parallel flaky α particles in the β grains form parallel α clusters. The strength and plasticity of the specimens treated over 1000 ℃ are poor, which should be avoided.

Key words: laser powder bed fusion, Ti-6Al-4V titanium alloy, heat treatment temperature, microstructure, mechanical properties