Effects of different active agents on the dynamic features and joint performance of full/partial-penetration laser welding of stainless-steel thick plates

This paper systematically investigates the effects of oxide active agents (SiO2, TiO2, Cr2O3), a rare earth active agent (CeO2), and a fluoride active agent (NaF) on the dynamic behavior of metal vapor/plasma, deep penetration keyholes, and the molten pool during laser full/partial-penetration welding of stainless-steel thick plates. This effectively suppresses the violent ejection of metal vapor/plasma, keyhole oscillation, and deformation, enhancing welding stability and increasing penetration depth. Among these, coating with a Cr2O3 active agent in the full-penetration welded state and coating with a SiO2 active agent in the partial-penetration welded state exhibited the most significant suppression effects on metal vapor/plasma ejection. Compared to samples without active agent coating, these treatments reduced ejection by 11.33% and 24.7%, respectively. Additionally, microstructure, mechanical properties, and elemental analysis indicate that active agents have a relatively limited impact on the microstructure and properties of full-penetration welded, while significantly improving those of the partial-penetration welded. The Cr2O3 active agent demonstrates the most pronounced effect, increasing tensile strength by 9.17%, compared to uncoated specimens. It also refines grain size and reduces the heat-affected zone. In contrast, the NaF active agent showed no significant effect on improving weld bead formation quality. This indicates that adding suitable active agents enhances welding stability and quality by regulating fluid behavior such as Marangoni convection. This study provides a solid experimental foundation for the theoretical development and industrial application of thick-plate laser welding technology.