Abstract: TC4 titanium alloy bars for aerospace fasteners were treated by solid solution treatment and aging, the miorostructure, hardness and room temperature tensile properties at different positions of the alloy bar were observed and examined. The results show that the microstructure and properties of the alloy bar after solid solution and aging treatments are significantly different from surface to core because of the cooling rate difference. After solid solution treatment and aging, the microstructure consists of stable equiaxed α, dispersed α′ martensite and substable β phases. There is no significant difference in morphology and content of secondary α phase in the end section of the specimen because of the similar cooling rate. From the upper part of the middle section to the core, the secondary α phase increases in content gradually, and the secondary α phase layer increases in thickness step by step and tends to be equiaxed. There is no obvious difference in microhardness at different positions of the end section, but the microhardness value from edge to core on the middle section shows a general decreasing trend, and the microhardness at edge on the middle section is close to that of the end section. Because of the slow cooling of the specimen core during solution treatment, the tensile properties of the whole specimen at room temperature are obviously poorer than those of the specimen with its core part removed.

Key words: TC4 titanium alloy for fasteners, solid solution treatment, aging, cooling rate, microstructure, properties