Strength and fatigue of 1500 MPa-grade Ti-5553 alloy bolt

• Ti-5553 alloy is the appropriate material for 1500 MPa-grade aeronautic fasteners. • Cold thread-rolling leads to the formation of shearing band in thread region. • The tensile-strength degradation of the bolt is caused by shearing band. • The bolt processes excellent tensile fatigue performance and shearing strength. Owing to the high bearing capacity, 1500 MPa-grade fastener fabricated by PH13-8 steel has been extensively used in the main bearing structure of aircraft. However, the density of the steel is as high as 8.2 × 10 3 kg/m 3 , which is adverse to the weight control of aircraft. By using 1500 MPa-grade Ti-5Al-5 V-5Mo-3Cr (Ti-5553) titanium alloy wire, we successfully manufactured the 12-point MJ6 × 1 Ti-5553 alloy bolt by hot uppset and cold thread-rolling. Although the shearing strength and the fatigue performance of Ti-5553 bolt are comparable to those of PH13-8 bolt, the tensile failure strength (TFS) is 11.3% lower. Furthermore, TFS of Ti-5553 bolt is also 11.3% lower than the ultimate tensile strength of bimodal Ti-5553 wire, exhibiting the obvious strength degradation. The strength degradation of the bolt is mainly caused by the stress concentration on the tip I-type mirco-crack evolved from the shearing band that forms during the cold thread-rolling. The excellent shearing strength and fatigue performance is strongly related to the bimodal structure. Our findings indicate that the shearing band in the root region of the thread should be eliminated by warm processing in order to improve the TFS of Ti-5553 bolt.