Study on the effects of Laser-TIG hybrid welding process parameters on keyhole stability and porosity mechanisms in 4J36 invar steel

Abstract

This study investigates the effects of laser power, welding speed, and welding current on melt pool fluid dynamics, Keyhole stability, and porosity by developing a multiphysics coupled numerical model and validating it with high-speed imaging experiments. A single-variable controlled experimental design was employed to address porosity defects encountered in the laser-TIG hybrid welding of 12 mm-thick Invar steel. The study found that increasing the laser power from 4 kW to 6 kW significantly raises the Keyhole collapse frequency and porosity. This is attributed to the increased recoil pressure and melt pool depth, which hinder bubble escape. Increasing the welding speed from 0.008 m/s to 0.05 m/s reduces porosity by enhancing the melt pool’s kinetic energy, which offsets interfacial forces, and by lowering heat input to Maintain Keyhole stability. Welding current exhibits a nonlinear effect on porosity, In the range of 100 A to 150 A, electromagnetic forces enhance melt pool stability and extend solidification time, promoting bubble escape. However, when the current increases from 150 A to 225 A, excessive heat input leads to local overheating and intensifies Keyhole instability. Finally, 1,000 frames of keyhole morphology during the stable stage were extracted, and analysis of keyhole collapse frequency was conducted to reveal the influence of welding parameters on porosity.