The thick TC4 titanium alloy sheets were welded by vacuum electron beam welding (EBW). The results indicated that the elongation of TC4 joint was significantly less than that of BM, indicating that ductility and plasticity of this joint was poor due to the formations of large quantity of the martensites in weld zone (WZ). Local heat treatment (LHT) led portion of α to be broken up, portion of α ′ became primitive β+α during a LHT process, resulting in staggered fine/short piece-shape phases; also α can be observed in the crystals' boundaries of β ; the tensile strength and elongation of LHT samples were significantly higher compared with those of same samples free of LHT. To have quantitative understanding of EBW of thick titanium alloy sheets and LHT effects, this paper has provided the technological and related theoretical basis to join TC4 sheets also further improve the mechanical performance of this joint. • TC4 titanium alloy sheets with 100 mm thickness were welded by vacuum EBW. • The phase transformation occurred free of the melting in HAZ. • Local heat treatment (LHT) led portion of α to be broken up, portion of α′ became primitive β+α. • Tensile strength and elongation of the LHT samples were significantly increased.. [ABSTRACT FROM AUTHOR]