TC4titanium alloy plate with 20 mm thick was welded by the vacuum electron beam

and effects of the electron beam current on microstructure and mechanical properties were investigated.The results show that the grain size of the welding joint is decreased with the increase of the penetration depth.With the electron beam current increase

the grain gradient is decreased.When the electron beam current is increased from 95 mA to 105 mA

size of the martensiteα′and intergranularαphase as well asα′lath in the upper of the seam is larger than that in the middle and lower of the seam.With the electron beam current increase

intergranularαphase becomes the wider andα′lath becomes the thicker.When electron beam current is decreased to 85 mA

absence of intergranularαphase andα′lath in the lower of the seam can be observed.When the electron beam current is 95 mA

strength of the seam reaches a maximum value of 1 265 MPa

which is the higher than that of the base metal

and the joint is characterized by mixed fracture with ductile fracture and quasi cleavage fracture.