Microstructure and mechanical property of Ti/Cu ultra-thin foil lapped joints with different weld depths by nanosecond laser welding

In present study, 50 mu m thick Ti/Cu pure metal ultra-thin foils are successfully lap-welded by a nanosecond fiber laser. The joints with adjustable depths are obtained by controlling the laser energy input precisely. The microstructure and mechanical properties of Ti/Cu joints with different depths are well analyzed, respectively. In the joint with smaller penetration depth of 10 mu m, thin band-like Ti/Cu intermetallic compounds (IMCs) are formed, while in the joint with a larger penetration depth of 40 mu m, thicker band-like Ti/Cu IMCs and sizable bright dendritic Ti2Cu phases are formed, since more Cu element are involved in the chemical reaction in the joint with penetration depth increasing. The tensile test results show that the weld with 10 mu m penetration depth has the best tensile strength up to 240 MPa, which is mainly due to less IMCs and low heat input in the weld. In addition, the fracture mode of the joint is classified into two models, including brittle quasi-cleavage fracture on the Ti side fusion zone (FZ) and ductile fracture on the Cu heat affected zone (HAZ), respectively, depending on the penetration depth above or below 30 mu m.