Reducing the underfill rate of pulsed laser welding of titanium alloy through the application of a transversal pre-extrusion load

A method for reducing the underfill rate of welded joints is proposed, and is based on the application of a transversal pre-extrusion load during pulsed laser beam welding of titanium alloy. By welding with a pre-extrusion load at different welding specific heat inputs, underfill defects can be reduced or even eliminated. A finite element simulation is employed to analyze the mechanism of this reduction. The calculated morphology of the weld cross-section and the total extrusion output agree well with experimental results. The reduction of underfill defects is mainly related to the normal hump of the soft materials generated at high temperature under a residual pre-extrusion load. The microstructures and mechanical properties in the welded joints are analyzed. The welded joints are stronger than the base metal because of the formation of the dominant martensite phase structure in the heat affected zone (HAZ) and fusion zone (FZ). Underfill defects in the weld zone cause a loss of tensile properties, and this loss can be compensated for by decreasing the underfill rate with a transversal pre-extrusion load.