航天超高强钢激光振镜扫描-TIG复合热源焊接关键技术及机理研究

Ultra-high strength steel 30Si2MnCrMoVE is mainly used in space products such as solid rocket motor shell, but the hardening tendency is large and the cold cracking sensitivity is serious. The traditional TIG welding process has complex procedure, low efficiency and high heat input, and the conventional laser and electron beam welding is highly efficient, but the temperature gradient is large and the overheating is serious. In this project, a laser galvanometer scanning-TIG hybrid welding method is proposed, on the basis of high efficiency and small heat input based on laser - TIG arc coupling effect, the molten pool is real-time stirred through laser beam swing / rotation, which promote weld pool convection, reduce the temperature gradient, accelerate gas escape; then the heat treatment is executed by using laser scan the weld zone in order to reduce the residual stress, escape diffusion hydrogen fully. The welding plasma behaviors and spectral characteristics were investigated by using high-speed camera and spectrometer; the oscillation behaviors and evolution process of molten pool were observed and analyzed; the interaction mechanism between the swing / rotation laser and the arc, the dynamic behavior of the molten pool and keyhole and the mass transfer and heat transfer behavior of molten pool are revealed, the internal correlation mechanism between the transient behaviors of remelting process and the porosity and crack under different scanning mode are investigated, further, the laser pre and post heat treatment effect and mechanism are also studied. Lastly, a new method of defect inhibition, weld formation and performance control is formed, which lays the foundation for the application of laser galvanometer scanning-TIG hybrid welding of aerospace super high strength steel and provides theoretical support.

超高强钢30Si2MnCrMoVE主要用于火箭发动机壳体等航天产品，但淬硬倾向大，冷裂敏感性严重。传统的TIG焊工序复杂、效率低、热变形大；激光焊效率高，但温度梯度高，过热严重。本项目提出激光振镜扫描-TIG复合焊接新方法，基于激光-电弧的耦合效应提高效率，减小热输入，通过激光束流的摆动/旋转搅拌熔池，促进熔池对流，降低温度梯度、加速气体逸出，采用激光扫描焊缝区进行预、后热处理，减小残余应力，扩散氢充分逸出。采用光谱仪及高速摄像等对复合焊接的等离子体形态、特征，熔池震荡及演变过程进行观察和分析，揭示摆动/旋转激光-电弧的相互作用机理，匙孔-熔池的动态行为及熔池内部的传质与传热行为，研究不同扫描模式下焊接快速熔凝瞬态行为与冷裂形成的关联机制，明确激光预、后热处理效果及作用机理，形成焊接缺陷抑制、焊缝成形和应力变形调控新方法，为航天超高强钢的激光扫描-TIG复合焊应用奠定基础和提供理论支撑。

传统的TIG焊工序复杂、效率低、热变形大；为应对当前复杂的国际形势，适应航天技术的快速发展，采用更加高质、高效的焊接方法迫在眉睫。本项目提出激光振镜扫描-TIG复合焊接新方法，通过激光束流的摆动/旋转搅拌熔池，促进熔池对流，降低温度梯度、增加间隙适应性。为深入理解扫描激光-TIG复合作用机理及焊缝成形控制方法，本课题展开了激光振镜扫描-TIG复合等离子体行为、作用机制及对焊缝成形的影响；不同扫描模式下快速熔凝过程的组织演变规律；激光扫描-电弧复合焊过程中的缺陷特征，形成机理及其抑制；柱等轴晶转变调控及机理等内容的研究。. 发现当激光功率为50%~80%时，电弧压缩最为明显，焊缝熔深最深。激光扫描可以促进熔区内等轴晶形成，细化晶粒，且连续激光能获得更细的晶粒和更多等轴晶，降低焊接残余应力和均匀化。当扫描速度为200mm/s时，焊缝内的大尺寸气孔数量明显减少，孔隙率降低到0.21%以下。而研究中也发现低速螺旋扫描能够最大限度的促进柱状晶向等轴晶转变，当扫描速度为10mm/s时，焊缝金属中等轴晶的比例甚至增加到65%，其延伸率增加到12.2%，提升了91%，断裂位置转变为母材区。在此基础上，提出了针对脉冲扫描激光的多次冲击-破碎效应气孔抑制机制，揭示了摆动激光-TIG复合焊接的柱等轴晶转变机制，提出了增加等轴晶比例的调控方法。. 通过上述的研究，解决了航天超高强钢扫描激光-TIG复合焊接的焊缝成形、组织演变和性能调控等关键问题，深入理解了摆动激光-TIG相互作用机理，揭示了摆动激光-TIG复合的气孔成因及抑制机理，柱等轴晶转变机制及调控方法，形成焊接缺陷抑制、焊缝成形和应力变形调控新方法，为航天超高强钢的激光扫描-TIG复合焊应用奠定基础和提供理论支撑。