旋转摩擦焊阻抗匹配特性研究

Rotary friction welding, being a solid state welding method, has been widely applied in civil engineering that shows the high quality of the joint, high efficiency and energy saving of the process. However, rotary friction welding is not well applied in aerospace industry owing to the lack of rules for process design (and reliable operation window). Thus arbitrary selection occurs on the operation parameters. Therefore, there is less confidence for the design department to choose such process for the joint manufacture. The rules for process design or operation window is supported by the process theory such as 'criterion' and 'characterization'. In friction welding, the requested heat for the joint formation is resulted from the 'friction impedance' to do work that releases heat. Thus, the key scientific issues are unveiled as the characterization of the friction impedance, i.e., characterization of friction impedance on distribution along friction interface and its evolution, and impedance matching criterion. This project focuses on the first stage of rotary friction welding process with experimental study as the main research methods. The work starts from the 'V-curve' study to locate the valley point as the 'criterion'. Thereafter, there comes into study of interfacial temperature field and corona bond evolution of the joint. By the combination study on the impedance evolution of friction, the 'heat pattern' of the joint is characterized and understood comprehensively. The theoretical models are then constructed for the heat liberation and optimal impedance matching criterion. The research will enrich the fundamentals of process theory on rotary friction welding and support the further study on joint reliability.

旋转摩擦焊在民用工业的广泛应用，充分显示其作为固相焊接所具备的高品质、高效与节能，但一直未能很好地应用到航空航天等高技术领域，因为缺少可信的工艺设计准则，从而导致规范选取的随意性和分散性。工艺的设计准则（和规范带），缘于"判据"、"特性"等工艺理论的支撑。摩擦焊接头成形所需要的热能，是界面"摩擦阻抗"做功耗散为热的结果。因此，摩擦阻抗特性研究，即摩擦阻抗分布、演变表征，以及最佳"阻抗匹配"判据等，就成为立项要解决的关键科学问题。本研究以旋转摩擦焊第一阶段为主要研究对象，以实验研究为主要手段，以 V 曲线研究为切入点，首先获得"V 曲线"极值点判据；进而深入研究界面温度场、塑性环演变；结合界面摩擦阻抗演变研究，表征并充分理解摩擦焊接头的"热流模式"；获得摩擦界面产热模型及最佳阻抗匹配判据的理论解析。研究成果将丰富摩擦焊制造供工艺理论基础，并为接头可靠性研究提供理论支撑。

本研究以旋转摩擦焊第一阶段为主要研究对象，以实验研究为主要手段，以V曲线研究为切入点，首先对多种材料体系的V曲线现象进行了实验探索，抓住V曲线阻抗匹配的本质，将实心棒试样的焊接时间与摩擦界面阻抗的分布及演变联系起来；通过模型简化，获得了管状结构试样V曲线极值点的影响因素和规律，找到最佳“阻抗匹配”点，建立了摩擦焊过程中第一阶段摩擦系数模型；在此基础上，建立了实心棒结构试样摩擦焊第一阶段的产热模型及温度场分布规律，建立了实心棒结构塑性环形核依据，解析了实心棒结构V曲线产生的机制；基于以此，对摩擦界面“阻抗做功”“耗散为热”现象作深入分析，以塑性环“形核—扩展”机理为对象，结合界面阻抗分布及演变规律，建立了塑性环扩展判据；利用获得的摩擦阻抗模型，借助数值模拟手段得到界面温度场分布及演变的数值解析。研究结果表明，对于管状结构，其最佳“阻抗匹配”点对应于线速度1m/s；对于实心棒结构，非红硬性材料（如SUS304）其阻抗演变随转速变化不明显；而对于红硬性材料（如GH2132），其最佳阻抗匹配点对应于外缘线速度0.3~0.6m/s，实心棒结构试样最佳阻抗匹配点的产生是由塑性环形核及演变规律在不同转速条件下发生变化的结果，本质上取决于第一阶段的产热分布；以此为基础深入解析了摩擦焊过程；将塑性环“形核—扩展”过程简化为两类，对于形核于边缘的塑性环，扩展至整个界面时呈现“鼓型”，在顶锻力作用下演化为接近鼓型的“直线型”热流模式。对于形核于中心的塑性环，扩展至整个界面时呈现“直线型”，在顶锻力作用下演化为接近鼓型的“剪刀型”热流模式；实心棒结构试样焊接过程中，阻抗(扭矩)峰值产生的机制是剪切变形加工硬化机制与再结晶回复软化机制综合作用的结果。研究成果对航空发动机、燃气轮机、潜艇推进器等盘－轴结构的摩擦焊设计与制造具有直接指导意义。