Microstructure and properties of titanium alloy electron beam weldments based on the different heat input conditions of the same line energy

Abstract

Electron beam welding (EBW) was applied to 20 mm thick marine high-strength titanium alloy Ti6321 with different heat input conditions of the same line energy, and microstructure, microhardness and tensile properties of the defect-free welded joints were examined. The results show that for small heat input (SHI) weld metal, martensite α′ phase was wide and intertwined and the residual β was relatively high. For large heat input (LHI), martensite α′ was relative small. Microstructure of the HAZ is inhomogeneous. For SHI, β phase collected in fusion line, and the heat affected zone of SHI had more residual β phase than that of LHI. XRD results indicate that the weld metal of LHI nearly consists of α′ martensitic phase but small quantity of β phase. However, the weld metal of SHI exists α′martensitic phase, β phase and some α phase. Microhardness values in the centre of weld metal of SHI decreases greatly because of α phase. While hardness of LHI weld metal is consistent. The fracture locations of LHI EBW joint specimens are in base metal, and the UTS of the joints reach 935 MPa. The fracture locations of SHI EBW joint specimens are in weld metal, and the UTS of the joints reach about 905 MPa.