Narrow gap multi-pass laser butt welding of explosion welded CP-Ti/Q235B bimetallic sheet by using a copper interlayer

Butt welding of explosion welded Ti/steel bimetallic sheet is still a challenging task due to brittle Ti-Fe intermetallic compounds (IMCs) generated in the transition zone between Ti and steel. Laser butt welding of Ti/steel bimetallic sheet was performed in this work. Preliminary results showed that cracks usually observed in the transition zone of arc welded joint could be effectively avoided by using laser welding and a copper interlayer. The key point was the elaborate control of the remolten volume of copper interlayer. The laser butt welded joint achieved was evaluated by using SEM, EDS and micro-hardness test. Tensile tests, bending tests and V-notched Charpy impact tests were conducted to reveal the mechanical properties. The tensile strength and impact absorbing energy of the butt joint were about 73% and 77% that of the CP-Ti/Q235B bimetallic sheet, respectively. The initiation position and propagation path of the crack were observed by high-speed imaging in both face and root bending tests. Finally, improvements brought by the laser butt welding process were concluded and strategies for improving the processing scheme in the future were suggested.