Abstract: Heat treatment experiments on the Ti-38644 titanium alloy with ϕ68 mm diameter bars were implemented at different temperatures, holding time and cooling methods. Effect of different heat treatment processes on the microstructure and mechanical properties of the alloy bars were studied. The results show that the content of the precipitated α phase increases with the solid solution temperature increase. With the increase of aging temperature, the precipitated α phase tends coarser, which result in the strength decrease, and the elongation increase. The strengthening effect is slackened. As the aging holding time extended, the precipitated α phase increase. The strength appeares a tendency to increase firstly and then decrease, and the plasticity changes in contrast. The effect of the solid solution cooling method on the alloy microstructure properties are notable. Due to the accelerates of the cooling rate, the β grains obtained is relatively small, and therefore, accounted for the strength raise up and the elongation decrease sharply. In conclusion, a better matching of strength and plasticity can be obtained in solution and aging heat treatment process (810 ℃×1 h, oil cooling+510 ℃×8 h, air cooling).

Key words: Ti-38644 titanium alloy, bars, heat treatment, microstructure, properties