Microstructure and mechanical properties of electron beam welded TC4/TA7 dissimilar titanium alloy joint

Abstract

Dissimilar titanium alloys TC4/TA7 are welded by using electron beam welding (EBW), and the microstructure and mechanical properties of welded joints are systematically investigated. Results show that the microstructure in different zones of welded joint is obviously different. The fusion zone (FZ) is mainly composed of fine α′ martensite. The heat-affected zone (HAZ) of TC4 side is composed of martensite, blocky α phase, original α phase and β phase. The HAZ of TA7 side consists of a small amount of martensite, blocky α phase and original α phase. TEM analysis shows that, due to the effect of modification welding, the martensite becomes coarser in the upper part of joint, and dislocations are generated in FZ. Element line scanning and elemental maps analyses indicate that the distribution of alloying elements is relatively uniform at joint interface, and no obvious segregation is occurred. The distribution of hardness in weld zones is ranked as follows: FZ > HAZ of TC4 side > TC4 base metal (BM) > HAZ of TA7 side > TA7 BM. The tensile strength of dissimilar joint is slightly higher than that of TA7 BM, while its elongation is slightly lower than those of the two BMs. The joint fails in the side of TA7 BM during stretching, and the morphology dominantly presents the characteristic of ductile fracture.