Effects of Si addition on mechanical properties of Ti–5Al–5V–5Mo–3Cr alloy

In this paper, the ageing response and the mechanical properties of Ti-5553 (Ti–5Al–5V–5Mo–3Cr) and Ti-5553s (Ti–5Al–5V–5Mo–3Cr–0.4Si) alloys are comparatively investigated. During ageing at 650 °C, the hardness of the alloys first increases in 30 min and remains constant from 1 h to 8 h, and then decreases with further increase the ageing time to 29 h. This variation is related to the chemical composition and the volume fraction of α phase. The mechanical properties of the 5 h aged Ti-5553 and Ti-5553s alloys are investigated, and the result shows that the ultimate tensile strength of the Ti-5553s alloy is higher than that of Ti-5553 alloy while the ductility of the Ti-5553s alloy slightly decreases. The tensile fracture of the Ti-5553s alloy shows a mixed model of intergranular fracture and cleavage fracture.