搅拌摩擦焊根部材料连接机理及性能调控方法研究

The ‘root flaw’ has detrimental effects on the mechanical performance and the in-service safety of the friction stir welds, but the root flaw could be hardly detected by the non-destructive tests. The formation of the root flaw is attributed to insufficient solid-state bonding between the seaming interfaces at the root region. However, the mechanism of material bonding at the root region has not been fully understood, which causes the lack of a solid theoretical basis for eliminating of the root flaw and controlling the performance of the welds. This project aims to investigate the solid-state bonding process at the root region during friction stir welding (FSW) by using both numerical simulation and experimental examination. The evolution of thermal-mechanical state variable, such as temperature, stress and plastic strain, at the root region under various welding conditions is to be quantified by experimental-validated numerical simulation, which will be used to analyze the material bonding process at the root region. The interplay between the thermal-mechanical state variables, material bonding behavior and mechanical performance is to be revealed in order to clarify the key influencing factor that governs the joint performance at root region. The processing control method for eliminating root flaws is to be established based on the material bonding mechanism and the key influencing factors, which will provide practical guides to the optimization of the welding parameters and welding tool design.

根部缺陷危害搅拌摩擦焊接头的承载能力及服役安全性，但依靠无损检测手段几乎无法检出。根部缺陷的产生根源是根部材料未发生完全连接，但搅拌摩擦焊过程中根部材料的连接机理尚不清楚，导致相关性能调控方法缺乏全面的理论支撑。本项目拟以高强铝合金为对象，采用计算机模拟与实验研究相结合的方法，研究搅拌摩擦焊中根部材料的连接机理及性能调控方法，定量表征不同焊接参数下根部材料经历的温度、应力、应变等物理条件，定量阐明搅拌摩擦焊过程中根部材料“从分离到结合”的固态连接动态物理过程，深入揭示根部材料经历物理条件、材料连接行为、根部力学性能之间的内在联系，明确控制搅拌摩擦焊接头中的根部性能的关键影响因素及其影响规律。基于对根部材料连接机理的准确理解，建立根部材料性能的调控方法，为搅拌头设计、焊接参数优化以及接头性能调控提供指导。

搅拌摩擦焊是一种先进的固态焊接技术，在航空航天、轨道交通等工业领域关键部件的制造中取得了广泛应用。搅拌摩擦焊接头中的根部缺陷，源于材料未完全连接，危害的承载能力及服役安全性；但搅拌摩擦焊过程中根部材料的连接机理尚不清楚，导致相关性能调控方法缺乏全面的理论支撑。本项目针对搅拌摩擦焊中根部材料的连接机理及性能调控方法进行研究。作为应用基础研究，本项目针对搅拌摩擦焊的建模仿真方法以及材料连接机理，均开展了较深入的研究。主要取得以下三方面进展：（1）进一步发展了基于计算流体力学的搅拌摩擦焊热-力过程的模拟仿真方法，阐明了搅拌针螺纹、搅拌头动态回抽等几何因素对搅拌摩擦焊温度场及材料流动场的影响规律；（2）提出了一种基于计算流体力学与表面微凸体变形法的搅拌摩擦焊材料连接行为分析方法，实现了搅拌摩擦焊过程中根部材料固态连接动态物理过程的准确定量预测；（3）提出了搅拌摩擦焊过程中塑性变形促进金属固态连接的一种物理机制——塑性流动有利于对接面获得有利的空间取向从而提高发生固态连接的比例。本项目的开展为研究搅拌摩擦焊根部缺陷的形成机理建立了新的定量方法，明确了抑制根部缺陷的新机制，完善了搅拌头设计、焊接参数优化以及接头性能调控的理论基础。