Characteristics of α Precipitated Phase and Tensile Properties of Cast Ti5553 Alloy

Ti5553 (Ti-5Al-5V-5Mo-3Cr) not only has high strength, but also has good mould filling fluidity, which is a typical high strength casting titanium alloy. The mechanical properties and deformation behavior of Ti5553 alloy mainly depend on the coupling effect of α phase characteristics and residual β matrix. The current research mostly focuses on the deformed alloy and the dependence of the mechanical properties of cast Ti5553 alloy on α phase characteristics is still unclear. In this paper, the room temperature tensile deformation behaviour of cast Ti5553 alloy and its relationship with α precipitated phase characteristics under different heat treatment process are investigated. The results show that: the HCP+FCC structure within the α lamellae of the alloy in the hot isostatic state activates numerous slip systems and the coordinated deformation of α twins and FCC phases leads to yield strength, tensile strength, and elongation of 955 MPa, 1020 MPa, and 10%, respectively; After solid solution aging, a large number of fine acicular α phases precipitate on the β matrix, and the alloy has high strength but very low ductility; the double annealed state alloy has the best strength-ductility match, and the yield strength, tensile strength, and elongation reach 1020 MPa, 1080 MPa, and 8%, respectively. The multiscale α lamellae intralaminar slip shear and α twins are the structural roots of their good strength-ductility.