Stepwise cooling spinning to achieve isotropic strength-ductility synergy of titanium alloy tube

To obtain high-strength titanium alloy thin-walled tubes, a new stepwise cooling spinning process was proposed, which involved multi-pass spinning with deformation temperature gradually reduced from the β phase region to the two-phase region. A setup for stepwise cooling was established, and Ti-6Al-4V thin-walled tubes with an ultimate strength of 1245 MPa and elongation of 7.51% along the rolling direction (RD) were successfully prepared via 5-pass spinning with a total thinning ratio of 80%. The microstructure, texture, and mechanical properties evolution in stepwise cooling spinning were analyzed. It is found that the stepwise cooling spinning results in a fine equiaxed structure, of which the primary α is strengthened by dislocation structures and the β phase is strengthened by precipitation of secondary α. Formation and deformation of the lamellar α weaken the overall texture but cause a local texture with <0001> // RD after the 3rd pass spinning. Meanwhile, the deformation of globularized α in the subsequent spinning results in two weak texture components with <0001> // normal direction (ND) and <0001> ⊥ ND. Thus, the strength and anisotropy of the tube increase with spinning passes, and then decrease.