Microstructure and mechanical properties of vacuum electron beam welded joints of Ti/Cu dissimilar metals

Abstract

Sheets of TC4 titanium alloy and T2 pure copper were joined by vacuum electron beam welding with an offset on the copper side. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to study the microstructure of the welded joint, and the composition of the intermetallic compounds (IMCs) at the reaction layer was studied by energy dispersive spectrometry (EDS) and transmission electron microscopy (TEM), followed by tensile testing to investigate the mechanical properties of the welded joints. The results show that electron beam welding can achieve an effective connection of Ti/Cu dissimilar metals. A multilayer structure composed of an IMCs layer, a final solidification zone, and a weld zone is formed at the Ti/Cu interface. The main composition of the IMCs layer is the faceted phase of TiCu and a small amount of the faceted phase of Ti2Cu, while the FS zone is composed of tiny equiaxed grains of copper. The tensile test results show that the ultimate tensile strength of the joints reaches 190 MPa, and the elongation rate reaches 4.27%. The joint presents brittle fracture characteristics with fracture occurring in the IMCs layer.