Study on the suppression of solidification cracks in narrow gap laser welding of high-strength steel based on dual-beam gradient control weld solidification.

Welding solidification cracks are considered as critical defects in narrow gap laser welding, and it is of utmost importance to develop reliable measures to suppress them. The fundamental approach to curbing solidification cracks lies in controlling the solidification behavior of the weld. A novel narrow gap laser welding technology is proposed to address this issue by controlling the solidification of the weld with double laser beam in this paper. The influence of process parameters on the suppression of welding solidification cracks is explored. Additionally, the mechanism behind the dual-beam laser's ability to suppress solidification cracks are comprehensively examined through weld formation, molten pool solidification behavior and microstructure evolution. The findings demonstrate that the energy matching of the dual-beam and the spacing between the beams are crucial factors that impact the effectiveness of welding crack suppression. When the beam spacing is greater than 6 mm, this method begins to work on suppressing welding solidification cracks. Three distinct effective modes of crack suppression are identified, namely molten pool expansion, gradient solidification, and weld remelting. Among these, the gradient solidification mode proves to be the most reliable method for suppressing welding solidification cracks, as it facilitates a transformation in the molten pool's solidification mode from "enclosed" solidification to "sequential" solidification. Compared to conventional single-beam Narrow Gap Laser Welding, this approach not only effectively suppresses welding solidification cracks but also improves welding efficiency by nearly doubling the filling speed. [Display omitted] • Inventing a narrow gap laser welding method based on dual-beam gradient control of weld solidification (NGDBLW). • Developing an in-situ observation method for molten pool solidification in weld cross-section. • NGDBLW has three effective modes to inhibit welding solidification cracks. • NGDBLW changes the growth mode of columnar crystals and enhances the tendency of growth along the y-axis. • NGDBLW significantly improves the efficiency of deposited metal. [ABSTRACT FROM AUTHOR]