高亮度激光厚板焊接中高强度、多角度蒸发致使匙孔界面形变更为复杂，熔池震荡加剧，凝固速率提高，从而易诱发形成气孔缺陷，成为影响焊接质量的关键问题之一。厚板激光焊时，匙孔形貌、光束与孔壁间能量耦合、流体压力、凝固速率等在Z向的特征变化对气孔缺陷的影响尤为突出。针对厚板激光焊接气孔形成过程这一科学问题，本项目拟采用原位观察、气孔Nano-CT三维空间精确表征等先进手段，并基于同步多曲面光束吸收与反射方法，构建多相、多自由界面三维瞬态气孔形成过程综合模型，研究不同激光入射角下熔池Z向的温度梯度、压力梯度、速度梯度及蒸发、流动、凝固等物理行为对气泡产生过程的影响，揭示气泡的生成、迁移及向气孔演化的时空路径，阐明匙孔波动、熔池流动、凝固速率梯度与气孔演化的内在关联机制，揭示气孔产生的临界条件及其控制因素，从而提出优化气泡逸出熔池的有效举措。本项目的研究可为推动高亮度激光在厚板焊接中的应用提供理论支撑。

During high-brightness laser welding on components with heavy section, keyhole-induced porosity become a key issue to determine weld quality. In this process, intensive and multi-angle evaporation of metal vapor leads to more complex deformation of keyhole, violent oscillation of molten pool and high cooling rate due to heavy sections, which tends to bring more pores. With the increase of thickness, the couple behavior between keyhole and laser beam, keyhole fluctuation, fluid pressure and solidification behavior of molten pool will play more important role in determining the formation of keyhole-induced pore in high-brightness laser welding. In this proposal, in-situ observation and a novel Nano-CT technique to represent three-dimensional 3D characteristics of porosity in space with high precision will be taken to study the defects. Meanwhile, based on the method of synchronous multi-curves absorption and reflection to laser beam, a multi-phase and multi-surface 3D numerical model will be established to reveal the scientific problems such as bubble formation, movement and evolution during laser welding. Based on experimental study and numerical model, the dynamic variation, solidification behavior in Z direction and the correlation regularity with porosity will be clarified at different radiation angles. To elucidate the temperature, pressure, velocity gradient in Z direction and fluid flow, evaporation and solidification and its correlation mechanism with the formation of porosity. The critical condition of porosity formation and controlling factors will be revealed, and then effective method to reduce pore and move out of molten pool will be put forward. The research results of this proposal can provide theory support for pushing further application of high-brightness laser welding on heavy sections.