基于热管/超声协同调控的搅拌摩擦焊接头特征及其演变机制

Friction stir welding (FSW) is a non-uniform and unstable process with thermal-dynamic , plastic rheology and heat transfer, mass transfer and phase transformation phenomenon, which make the joint characterized with asymmetricity, heterogeneity and discontinuity in temperature, rheology, microstructure and performance. It is also found that the joint often breaks in the "weak bonding" resulting low strength level. At present, as the thermodynamic coupling process of FSW is very complex, it is lack of comprehensive, in-depth understanding as well as active and effective control for the joint feature. The project intends to select magnesium alloy as the welding object and carry out the study on characteristics and its evaluation mechanism of the joint fabricated by FSW via heat pipe / ultrasonic collaborative control. The heat sink is composed of heat pipe and welding, which is used to cool both sides of weld beside the stirring tool . " Ultrasound / heat sink " composite slider is used to trace and cool weld rear. Based on the strengthen heat transfer effect of the heat pipe and the heat sink, as well as ultrasonic vibration and thermal effect along the thickness of the weld, we can realize the active and collaborative control for FSW process and the joint characteristics. The project will focus on the study about microstructure and performance of the joint welded via heat pipe / ultrasonic collaborative control, and reveals its evolution mechanism. Aiming to the "joint feature", "weak bonding" and their evolution mechanism, this project will also explore the law of heat pipe / ultrasonic collaborative control. This research has important theoretical and practical significance to FSW welding method and mechanism.

搅拌摩擦焊（FSW）是一个不均匀、非稳态的热力学、塑性流变学和传热、传质与相变过程，导致了接头温度、流变、组织和性能的非对称、非均匀和非连续性，且因"弱连接"导致接头强度系数下降。FSW的热力耦合过程极为复杂，目前尚未全面、深入地认识接头特征，且缺少主动、有效的控制。本项目拟以镁合金为焊接对象，系统开展热管/超声协同调控FSW的接头特征及其演变机制研究，将热管与焊件构成热沉在两侧强制冷却焊缝，同时运用"超声/热沉"复合滑块在焊缝后侧进行跟踪，综合利用热管及滑块热沉的强化换热效应，以及沿焊缝厚度方向为主的超声波振动和热效应，实现对FSW过程及接头特征的主动协同控制。重点研究协同调控作用下FSW接头组织和性能特征，并揭示其演变机制；针对常规FSW的"接头特征"、"短板效应"及形成机制，探索热管/超声协同调控的规律。本研究对FSW焊接方法和机理研究具有重要的理论和实践意义。

搅拌摩擦焊（FSW）是一个不均匀、非稳态的热力学、塑性流变学和传热、传质与相变过程，导致了接头温度、流变、组织和性能的非对称、非均匀和非连续性，且因“弱连接”导致接头强度系数下降。FSW的热力耦合过程极为复杂，目前尚未全面、深入地认识接头特征，且缺少主动、有效的控制。本项目以镁合金为焊接对象，系统开展了热管/超声协同调控搅拌摩擦焊接FSW的接头特征及其演变机制研究，将热管与焊件构成热沉在两侧强制冷却焊缝，综合利用热管的强化换热效应，以及沿焊缝厚度方向为主的超声波振动和热效应，实现对FSW过程及接头特征的主动协同控制。重点研究协同调控作用下FSW接头组织和性能特征，并揭示其演变机制；针对常规FSW的“接头特征”、“短板效应”及形成机制，探索热管/超声协同调控的规律。研究结果表明，超声/热管协同控制条件下，各特征点的焊接热循环峰值温度和高温停留时间均明显降低，前进侧与后退侧的峰值温度更加接近，可有效控制动态再结晶过程的晶粒粗化和弥散强化相的重溶。常规条件下，在厚度方向上，针影响区（PAZ）硬度较低，沿厚度方向上硬度呈V型分布。施加超声/热管后，由于焊针影响区材料的流动性增强以及焊接热量得到有效扩散，晶粒细化，硬度得到提升，三维尺度方向的力学均匀性也得到提高，有效减小了弱连接倾向。本项目的研究成果对FSW焊接方法和机理研究具有重要的理论和实践意义。