Combined effect and mechanism of thermal behaviour and flow characteristic on microstructure and mechanical property of oscillation laser-welded of IN718

An oscillation laser beam was conducted to enhance the mechanical property of Inconel 718 joints. The dynamic behaviours of molten pool on the microstructure and mechanical property of joints were investigated. The results showed that the improvement of Laves phase and the tensile property depended on the flow and thermal behaviours of molten pool. Compared with conventional laser welding, the maximum flow velocity on the surface of molten pool increased by 375.5%(150 Hz), which indicated the dendrites received greater bending stress to break more easily, resulting in the homogenisation of element. In addition, the oscillation laser beam decreased the temperature gradient from 218.5°C/mm to 73°C/mm, and the cooling rate of 150 Hz in the centre and edge of molten pool increased by 64.4% and 111.9%, which hindered the segregation phenomenon during the element diffusion to restrain the formation of Laves phase in the eutectic reaction.