Fracture surface characterization of laser welding processed Ti alloy to stainless steel joints

Abstract

The laser welding of Ti6Al4V alloy to 304 stainless steel using a 1-mm-thick Cu interlayer was developed by changing the laser power. The fracture characteristics of joints were analyzed by SEM, EDS, and XRD. The fracture examinations indicated that both the joint strength and the fracture occurrence location in the joints depend on the laser power settings. The optimal value for the maximized tensile strength of the joints, up to 300 MPa, was obtained at a power of 4 kW. Increasing the laser power by 4 kW increased the tensile strength; it decreased as the laser power exceeded 4 kW. In the 4-kW samples, the fracture characterization indicated that the higher remaining Cu deposited on the Ti sheet that caused the fracture path tended to make the fracture propagate toward the Cu interlayer. The fractography investigations illustrated that the fracture surface of a 4-kW joint had a greater rough area than that of either the 3- or the 6-kW joints. The XRD results demonstrated that the most of solid solution phases, such as αTi, (V), and (Ni) coexisting with various types of Al-intermetallics could occur on the fracture surface of a 4-kW weldment.