Effect of electron beam welding on the microstructures and mechanical properties of thick TC4-DT alloy

Electron beam welding (EBW) was applied to 50 mm thick damage-tolerant Ti-6Al-4V (TC4-DT) alloy, and microstructure, microhardness and tensile properties of the defect-free welded joints were examined. The results indicated that the microstructure of the base metal is composed of primary alpha phases and the lamellar (alpha + beta) bimodal structure. For the EBW joint, martensite basketweave microstructure is formed in fusion zone (FZ). Moreover, the heat affected zone (HAZ) near FZ consists of acicular martensite and a small portion of primary alpha phase. The HAZ near base metal consists of primary alpha phase and transformed beta containing aciculate alpha. It is found that the boundary of the two portions of the HAZ was dependent on the p phase transus temperature during weld cooling. Microhardness values for FZ and HAZ are higher than that of base metal, and there are the peak values for the HAZ near the weld metal. The fracture locations of all the EBW tensile specimens are in base metal, and the ultimate tensile strength of the joints may reach about 95% of the base metal. In addition, with the depth increasing along the weld thick direction, the grain size of the FZ decreases and microhardness increases. (C) 2011 Elsevier Ltd. All rights reserved.