To obtain high-quality welded joints with low heat input and high welding efficiency, a laser oscillating mode was proposed for welding D406A ultra-high strength steel (UHSS). The effect of four oscillating modes on morphology, microstructure and mechanical properties of the 3.5 mm-thick UHSS welded joints were discussed, including transverse, longitudinal, circular and without oscillation. The morphologies of the welded joints with different oscillating modes were significantly different. Among them, circular oscillation obtained the deepest weld penetration, and an asymmetric phenomenon of cross-section was observed. Furthermore, both transverse and circular oscillation obtained equiaxed grains, while circular oscillation had the finest columnar grains and the largest equiaxed grain area. Subsequently, mechanical properties of the welded joints with circular oscillation were improved obviously, which has the highest tensile strength of 809.44 MPa and the largest ductility of 21.8%. In comparison to without oscillation, the tensile strength and ductility were increased by 9.58% and 11.4% respectively. This study provides guidance for the selection of optimal oscillating modes for laser welding of UHSS.

为获得低热输入和高焊接效率的高质量焊接接头，提出了一种激光振荡模式焊接D406A超高强度钢（UHSS）。讨论了四种振荡模式对 3.5 mm 厚 UHSS 焊接接头的形貌、显微组织和力学性能的影响，包括横向、纵向、圆形和无振荡。具有不同振荡模式的焊接接头的形貌有显着差异。其中，圆形振荡获得最深的焊缝熔深，并观察到截面不对称现象。此外，横向和圆形振荡均获得等轴晶粒，而圆形振荡具有最细的柱状晶粒和最大的等轴晶粒面积。随后，圆振荡焊接接头的力学性能明显提高，最高抗拉强度为809.44 MPa，最大延展性为21.8%。与无振荡相比，抗拉强度和延展性分别提高了9.58%和11.4%。本研究为超高速钢激光焊接最佳振荡模式的选择提供了指导。