Modeling the role of beam oscillation in reducing element segregation during dissimilar laser welding of steel and nickel alloys

This study presents a three-dimensional numerical model to investigate the influence of laser beam oscillation on element segregation during the welding of 9Cr steel and nickel-based dissimilar alloys. The model simulates molten pool dynamics and solidification behavior under three oscillation conditions: no oscillation, circular oscillation, and infinity-pattern oscillations. Without oscillation, significant Fe segregation occurs on the 9Cr steel side, with blocky patterns in the upper weld and band-like formations in the middle, reaching an area fraction of 25.82 %. Circular and infinity-pattern oscillations effectively reduce segregation to 7.08 % and 4.48 %, respectively. The segregation is driven by the interplay between molten pool flow and solidification dynamics, with Marangoni forces drawing Fe-rich melt toward the 9Cr side. Laser beam oscillation enhances molten pool convection, disrupting Fe accumulation and promoting mixing. Notably, infinity-pattern oscillation, characterized by higher velocity and greater backward displacement, provides superior post-heating and stirring effects. At 50 Hz frequency and 0.6 mm amplitude, it achieves the most effective suppression of Fe segregation. These findings provide valuable insights into optimizing oscillation strategies for improving weld quality in dissimilar metal joining.