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<p>The influence of oscillation amplitude on molten pool thermal history, weld morphology characteristics, microstructural evolution, and mechanical properties during laser oscillating welding of QP980 steel was systematically investigated. Results show that laser beam oscillation significantly regulates molten pool thermomechanical behavior through optimized spatial energy distribution, thereby enabling microstructural reconstruction and joint performance enhancement. As the oscillation amplitude increases from 0 to 0.8&#xa0;mm, the molten pool duration extends to 1.7 times the original value, while peak temperature and average cooling rate decrease by 19% and 39%, respectively. This thermal regulation promotes weld surface width expansion from 0.72 to 1.07&#xa0;mm. The welding mode undergoes a progressive transition from keyhole mode → transitional mode → conduction mode. This transformation effectively suppresses porosity defects, substantially reducing porosity from 1.8% to 0.15%. Microstructural analysis indicates that oscillation modifies the maximum temperature gradient direction within the molten pool, facilitating preferential growth of coarse columnar grains along the welding centerline to establish load-transfer-favorable crystallographic orientations. The synergistic effects of these factors substantially improve joint mechanical properties: lap joint shear load increases by 81.5% (7.6 → 13.8&#xa0;kN), and fracture elongation is enhanced by 135% (0.98 → 2.3&#xa0;mm). The operational principles of laser oscillation parameters on the welding quality of QP980 steel&#xa0;were elucidated, providing theoretical foundations for joining process optimization.</p>

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Effect of weld pool thermal history on microstructure and mechanical properties of laser oscillating welded QP980 joints

  • 期刊论文

  • 发表日期：

    2025年12月25日

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  • Jing-Wei Yang,
  • Xu-Yang Liu,
  • Jian Qiao,
  • Ji-Heng Wang,
  • Zhan-Kun Weng,
  • Jia-Le Chen,
  • Ze-Ming Guan,
  • Zong-Ye Ding

摘要

The influence of oscillation amplitude on molten pool thermal history, weld morphology characteristics, microstructural evolution, and mechanical properties during laser oscillating welding of QP980 steel was systematically investigated. Results show that laser beam oscillation significantly regulates molten pool thermomechanical behavior through optimized spatial energy distribution, thereby enabling microstructural reconstruction and joint performance enhancement. As the oscillation amplitude increases from 0 to 0.8 mm, the molten pool duration extends to 1.7 times the original value, while peak temperature and average cooling rate decrease by 19% and 39%, respectively. This thermal regulation promotes weld surface width expansion from 0.72 to 1.07 mm. The welding mode undergoes a progressive transition from keyhole mode → transitional mode → conduction mode. This transformation effectively suppresses porosity defects, substantially reducing porosity from 1.8% to 0.15%. Microstructural analysis indicates that oscillation modifies the maximum temperature gradient direction within the molten pool, facilitating preferential growth of coarse columnar grains along the welding centerline to establish load-transfer-favorable crystallographic orientations. The synergistic effects of these factors substantially improve joint mechanical properties: lap joint shear load increases by 81.5% (7.6 → 13.8 kN), and fracture elongation is enhanced by 135% (0.98 → 2.3 mm). The operational principles of laser oscillation parameters on the welding quality of QP980 steel were elucidated, providing theoretical foundations for joining process optimization.