Objective Problems exist in weathering steel T-joints of high-speed train bogies, such as welding difficulty and challenges in achieving double-sided forming with single-sided root welding. To improve the adaptability to assembly welding gaps and the weld formation quality of T-joints, it is necessary to conduct research on oscillating laser welding technologies.

Method A research framework of 'process parameter optimization–organizational performance characterization–mechanism correlation analysis' is adopted. Process optimization experiments are carried out using the amplitude and frequency of circular oscillation as variables to screen the optimal parameter combination. On this basis, 0 mm and 2.5 mm two typical assembly gap joints are selected. The microstructures of various regions are observed using optical microscopy and SEM (scanning electron microscopy), and the hardness distributions in the arc zone and laser zone are measured using a Vickers hardness tester, thereby establishing the correlation mechanism between process parameters and joint performances.

Result & Conclusion  When the circular oscillation amplitude is 0.5 mm and the frequency is 200 Hz, the weld formation is optimal to accommodate assembly gaps within 2.5 mm. The weld is fully penetrated on the backside without weld bead accumulation, and the front-side formation is uniform and continuous. The weld zones for both 0 mm and 2.5 mm gaps consisted of 'ferrite + pearlite columnar grains,' with finer grains in the laser zone than in the arc zone, while the overheated zone consisted of 'bainite + pearlite coarse grains.' Compared with the 2.5 mm gap, the average weld hardness of the 0 mm gap is approximately 10% higher, and the hardness in the laser zone is about 20 HV higher.