采用小孔和孔内等离子体逐层截面直接观测技术的激光深熔焊接铝合金小孔形成机理研究

In order to solve such two important scientific problems as the formation mechanism of the keyhole and the keyhole effects in deep penetration laser welding of metal materials, such two key technology breakthroughs as the direct observation of the keyhole and the direct detection of the plasma exsisted in the keyhole are made in this project by proposing two kinds of specially-designed experimental setups during deep penetration laser welding of aluminum alloys. Used these experimental setups, the global keyhole shape can be determined through direct layer-by-layer observation of the crosssectional keyhole profile with a high speed camera, and the spectrum emitted anywhere from the plasma exsisted in the keyhole can also be directly detected by a multi-channel spectrometer. Based on the above experimentally-obtained crosssectional keyhole profile，a true 3D keyhole can be reconstructed. Then, combined with the above experimentally-detected spectrum data, such three mathematical models as a model of multiple reflections and absorptions, a model of plasma absorption, and a model of heat & mass tranfer, are established by tracing a ray of Gaussian beam in the 3D keyhole. Solved these models, both the laser energy intensities absorbed on the keyhole wall from Fresnel absorption & inverse bremsstrahlung absorption of the plasma and the heat influx losted on the keyhole wall due to conduction and convection, can be calculated. Compared the absorbed laser energy intensities with the losted heat influx at the same place on the keyhole wall, the mechanism of energy balance on the keyhole wall is studied..In order to break the technical limitation on the direct measurement of the pressure of the plume in the keyhole, a simulation detecting method of the plume pressure is put forward and the corresponding experimental setup is designed. With this setup, a hole forms when the gas with high pressure injects the liquid used such as water and liquid Hg, from which the relationship between the hole shape and such parameters as the injection pressure of the gas, its moving speed and the physical propertoies of the liquid, is investigated. From the keyhole shape observed by the above experimental setup in deep penetration laser welding of aluminum alloys, the injection pressure of the plume in the keyhole can be calculated by analogy analysis, which can be used to study the mechanism of pressure balance in the keyhole..This project has important guiding significances for better understanding the mechanism of deep penetration laser welding.

围绕激光深熔焊接小孔形成机理和小孔效应重要科学问题，突破金属材料激光深熔焊接小孔和孔内等离子体直接观测关键技术，采用特殊设计的实验装置，通过高速摄像机和多通道光谱仪，实现铝合金激光深熔焊接小孔和孔内等离子体辐射光谱的全方位直接观测。依据逐层观测得到的小孔截面形状，重构真实三维小孔；结合孔内等离子体辐射光谱检测数据，通过跟踪高斯光束在小孔内的反射传输过程，建立激光深熔焊接小孔孔内多次反射吸收、等离子体反韧致辐射吸收及传热传质数学模型，系统研究小孔孔壁上的能量平衡机制；突破激光深熔焊接小孔内金属蒸汽压力直接检测关键技术，提出一种小孔孔内压力模拟检测实验方法，研究小孔形状与气体喷射参数、液体介质物理性能之间的关系，根据实验观测得到的激光深熔焊接铝合金小孔形状，通过类比分析，计算小孔孔内蒸汽压力，深入研究深熔焊接小孔内的压力平衡机制。本项目的实施，对加深激光深熔焊接机理的理解具有重要指导意义。

围绕激光深熔焊接小孔形成机理和小孔效应关键科学问题，以实现金属材料激光深熔焊接小孔形状和孔内等离子体辐射光谱信息全方位直接观测为突破口，采用特殊设计的复合试件和实验装置，应用高速摄像机和光谱仪逐层观测得到了金属材料激光深熔焊接小孔的截面形状和等离子体辐射光谱信息。然后依据逐层观测得到的小孔截面形状，通过重构获得了真实的三维小孔；通过跟踪高斯光束在真实三维小孔内的反射传输过程，建立了激光深熔焊接小孔孔壁上的多次菲涅尔（Fresnel）反射吸收及传热数学模型，开发了相关算法，系统研究了小孔孔壁上的能量平衡机制；提出了一种小孔孔内压力模拟检测实验方法，实现了激光深熔焊接小孔内金属蒸汽压力模拟检测，确定了小孔形状与气体喷射参数、液体介质物理性能之间的关系，通过类比实验观测得到的激光深熔焊接金属材料小孔形状，计算了小孔孔内的蒸汽压力、流体动压力，深入研究了深熔焊接小孔内的压力平衡机制；基于本项目能量平衡相关研究成果及算法，计算得到了金属材料激光焊接温度场、应力应变场，系统研究了金属板材激光焊接变形。.本项目实施期间，共获得中国发明专利10项，发表SCI收录论文6篇，培养博士研究生2名、硕士研究生6名。.本项目的实施，对加深激光深熔焊接机理的理解具有重要指导意义。