窄间隙光纤激光-电弧复合焊接关键技术与机理研究

The narrow gap arc welding that is commonly used in present stage has been one of the main limits to improve the joining quality and efficiency of large-thickness structures in shipbuilding, nuclear facilities and oil pipelines because of big heat input, unsatisfied performance and large distortion. This project puts forward to a new technique that is named as narrow gap fiber laser-MIG arc hybrid welding. Both the advantages of fiber laser with excellent beam quality and laser-arc hybrid welding with high stability, deep penetration and good performance are integrated in this new welding process so that it has the potential to narrow the groove gap, reduce the welding passes, and improve the process stability and joint quality. Some key scientific questions related to this technique are considered in this project. The first important research is to study the effects of the space constraint caused by the narrow gap on the dynamic behavior and physical parameters of both arc column and laser-induced plasma during the welding. According to the recorded data, the laser-arc interaction mechanism in narrow gap is to be revealed, and the reason why the process stability is enhanced by laser-arc interaction will be discussed. Subsequently, the effects of laser-arc interaction on the molten pool behavior in narrow gap, the microstructure characterization of different zones in the joint and the defect of side-wall incomplete fusion, as well as the relationship between them with joint mechanical properties. Finally, the method and empirical formula for suppressing side-wall incomplete fusion are to be proposed, and the strategy for regulating and controlling microstructure-mechanical properties of the joints is to be developed too by the strength-toughness reinforced principle. The results would be interesting for enriching the fundamental theory of narrow gap welding and laser welding.

现有电弧窄间隙焊接工艺存在热输入大、接头性能不理想和结构变形大的问题，是制约船舶、核设施、石油管道等领域大厚度接头结构制造质量和效率提升的主要技术瓶颈之一。为此，本项目提出开发窄间隙光纤激光-MIG电弧复合焊接新工艺，利用光纤激光优异的光束质量和复合焊接的技术优势来缩小坡口间隙，减少焊道数量，提高工艺稳定性和接头质量。本项目将围绕其中的关键科学问题进行研究，重点研究窄间隙空间拘束效应对激光等离子体、电弧动态行为和物性参数的影响规律，明晰窄间隙条件下的激光-电弧相互作用机理，探讨激光-电弧相互作用对窄间隙工艺的稳定增强机制。在此基础上研究激光-电弧相互作用对窄间隙熔池动态行为、焊缝微观组织、侧壁未熔合缺陷的影响规律，及其和接头力学行为的相互关联。最后归纳总结侧壁未熔合缺陷抑制方法或理论计算公式，基于接头强韧性增强原则提出接头组织性能调控机理。研究结果对丰富焊接基础理论具有重要意义。

通过开发窄间隙光纤激光-电弧复合焊接新工艺，实现了大厚板的高效率、高质量焊接，掌握了窄间隙条件下复合焊接过程稳定性、焊缝成形、微观组织和接头力学性能的变化规律，明晰了空间拘束下的激光-电弧相互作用机理，及其对侧壁未熔合缺陷的影响机制，提出了对应的抑制方法或经验公式和基于接头强韧性增强的组织性能调控机理。研究结果不但为大厚度接头高质量焊接提供了一种新方法，而且丰富了窄间隙焊接和激光-电弧复合焊接基础理论。主要研究结果如下：.(1) 将复合焊接坡口宽度成功压缩至6mm，远低于窄间隙电弧焊接坡口宽度(10-18mm)，大幅度提高了焊接效率和接头质量。采用6mm矩形坡口，以9道焊缝实现了40mm低碳钢的复合焊接，接头组织性能分布均匀，焊缝截面沿厚度方向不同填充焊道的显微硬度值差别不超过15 HV0.2，接头抗拉强度和冲击吸收功分别比母材提高了49%和60%以上。.(2) 窄间隙复合焊接热源熔化能增量比开放空间复合焊接提高3-12%，焊缝熔深增加10-22%。发现空间约束效应是提升窄间隙复合热源能量传输效率，增加焊接熔深的关键机制。.(3) 提出了表征复合焊接过程稳定性的电弧电信号近似熵半定量分析新方法。近似熵值越小，焊接过程越稳定。通过该方法明确了空间约束效应对激光-电弧复合焊接过程稳定性的增强程度和作用机制。计算结果表明窄间隙复合焊接近似熵值比开放空间复合焊接低1-16%，焊接过程稳定性明显增强。.(4) 以焊缝表面下凹深度为因变量，采用量纲分析方法建立了窄间隙激光-电弧复合焊接未熔合缺陷定量预测模型，并基于该模型得到两套未熔合缺陷抑制方案。.(5) 研究发现电弧模式和保护气体对窄间隙复合焊接接头组织性能有明显影响。其中，CMT（Cold Metal Transfer）电弧因为热输入低于常规脉冲电弧和短路电弧，其复合焊接接头具有最小的焊缝平均晶粒尺寸、最高的针状铁素体含量和最佳力学性能。其次，随着保护气体中CO2含量增加，窄间隙复合焊接熔池冷却速度加快，Mn元素烧损加剧，最终导致接头针状铁素体含量减少，力学性能下降。

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