Formation of weld and mechanical properties of Ti6Al4V thin plate by pulse laser welding

In order to improve defects such as welding burn through and leakage caused by tooling error or burr in laser welding of titanium alloy sheet, a pulse laser welding experiment was carried out on 1.2 mm thick Ti6Al4V sheet with a fiber laser. Effects of pulse frequency, butt clearance and laser peak power on formation of weld were analyzed. Microstructure and mechanical properties of welds with good appearance were tested, and the best welding parameters suitable for butt welding of Ti6Al4V thin plate were determined. The results showed that excellent weld quality could be obtained by a pulse laser welding process with a pulse frequency of 40 Hz, a duty cycle of 60%, a laser peak power of 2.0 kW, a spot diameter of 0.7 mm and welding speed of 1.8 m/min. The weld consisted of thick columnar β grains and acicular α′ phase, and short needle shape α′ phase formed in heat-affected zone. With increase of peak power, microhardness of weld increased obviously, but tensile strength decreased gradually. Strength of weld under the optimal welding parameters could reach 98% that of base metal. The surface of tensile fracture was flat and regular, fracture surface to direction of tensile axis showed 45°, and fracture contained a large number of dimples.Highlights: (1) Pulse laser welding experiment with a specific pulse waveform and large spot diameter was carried out on Ti6Al4V thin plate, and formation quality of weld was improved.(2) Considering influence of tooling clearance during thin plate butt welding and reserving clearance before the experiment, the optimal welding parameters of pulse laser welded Ti6Al4V thin plate were explored.