Achieving superior mechanical properties in electron beam welded joints of Ti-5Al-5Mo-5V-1Cr-1Fe alloy thick plate using novel annealing treatments

Abstract

The strength reduction of Ti-5Al-5Mo-5V-1Cr-1Fe alloy (Ti-55511) thick plate joints after electron beam welding (EBW) largely limited their engineering application. In this study, three annealing treatments, including single, double and triple annealing, after EBW were designed to regulate the morphology and distribution of α phase in the Ti-55511 alloy weld 30 mm in thickness, which largely enhanced the joint strength. Among three annealing treatments, double annealing enhanced the joint strength most, with the increase in the yield and tensile strengths from 873 MPa and 919 MPa for the as-welded joint to 1025 MPa and 1095 MPa for the annealed joint, respectively, which were even superior to those of the base material. The great increase of the joint strength after double annealing was mainly attributed to the alternate distribution of the newly formed lamellar α and acicular secondary α phase, which was achieved via the transformation and growth of punctated martensite (FCC) phase during the first annealing and the precipitation of acicular secondary α phase from the metastable β grains during the second annealing. The microstructural evolution during welding and subsequent annealing was discussed. This study provides a novel annealing treatment to improve the strength of titanium alloy EBW joints.