Microstructures and mechanical properties of a titanium alloy thick plate joint after electron beam welding plus solution-aging

A thick plate of Ti–6Al–2Zr–2Sn–3Mo–1.5Cr–2Nb (TC21) damage-tolerant alloy was electron-beam welded and the joint was treated via solution aging. The microstructural characterizations and mechanical properties of the welding and solution-aging states were also investigated. The results indicated that in the welding state, the fusion zone (FZ) is composed of grain boundary α, martensite α′, and residual β phases. The heat-affected zone (HAZ) consists mainly of primary α, martensite α′, and residual β phases. The microhardness value of the FZ is higher than that of HAZ and base metal (BM), and the hardness value of the welded joint from the FZ to BM fluctuates greatly. The ultimate tensile strength (UTS) and elongation (EL) of the welded joint are 1183 MPa and 7.5%, respectively. The weak spot of impact toughness on the welded joint is the FZ, about 11 J. After solution aging, the martensite α′ in the FZ and HAZ transforms completely into lamellar α. Compared with the welding state, the fluctuation in the hardness value markedly decreases. The UTS and EL of the welded joint are 1145 MPa (a 3% decrease) and 12.5% (a 66.7% increase), respectively. The impact toughness of the FZ is 27 J, an increase of approximately 145%. The strength of the welded joint is well matched with their plasticity and toughness.