高速列车用铝合金搅拌摩擦焊接头超高周疲劳行为与剩余寿命研究

Based on the intrinsic advantages such as high efficiency, low cost, superior quality and environmentally friendly, friction stir welding (FSW) will become the predominant joining technology of next generation high-speed trains. With the high-speed trains operating speed increased, fatigue property of welded joints at very high cycles is one of the most important prerequisite for the security service. Current researches mainly focus on fatigue failure of FSW joints in low and high cycles, ignoring the risk of very high cycle fatigue (VHCF) failure. This project proposed for FSW joints of aluminum alloys to explore the characteristics and fracture mechanism of VHCF behavior, and clarify the effects of base metal state, welding parameters, post-weld treatments and environments on the VHCF properties. Further, physical damage process and micromechanism as well as damage equation of FSW joints will be investigated to predict the damage state and residual life of the joints. The completion of this project is beneficial for the understanding of VHCF damage essence of FSW joints, and enriches VHCF failure theory of welded joints, promoting the mature application of FSW in high-speed train manufacturing and providing scientific basis for safety service and reliability assessment of high-speed trains.

基于高效率、低成本、优质、环保等优势，搅拌摩擦焊（FSW）必将成为新一代铝合金高速列车的主导连接技术。随着高速列车运营速度的不断提高，焊接接头的超高周疲劳性能是保证列车安全服役的重要前提。当前对高速列车铝合金FSW接头的研究主要针对于高、低周疲劳失效问题，忽视了潜在的超高周疲劳失效风险。本项目拟针对高速列车铝合金FSW接头的超高周疲劳问题开展研究，明确其超高周疲劳特性，揭示超高周疲劳断裂机理，阐明母材状态、焊接条件、焊后处理和环境介质对接头超高周疲劳性能的影响，厘清接头超高周疲劳物理损伤过程和微观损伤机制，以及构建超高周疲劳损伤方程，实现FSW接头的损伤预测和剩余寿命评估。本项目的完成可加深对铝合金FSW接头超高周疲劳损伤本质的理解和认识，丰富焊接接头超高周疲劳断裂理论，为FSW在高速列车制造中的成熟应用提供理论支持，并为高速列车的安全服役和可靠性评定提供科学依据。

高速列车运行速度的不断提高有可能带来潜在的超高周疲劳失效风险，本项目以铝合金搅拌摩擦焊接头为研究对象，建立了铝合金接头多尺度第二相与疲劳裂纹扩展速率之间的多元非线性关系模型；研究了接头超高周疲劳断裂特性，发现了疲劳裂纹向内转移的现象，结合微观组织与断口分析，揭示了内部疲劳裂纹萌生机理和扩展过程；研究了FSW接头在疲劳加载过程中微电阻的变化规律，为疲劳在线监测和诊断的形成提供了依据；借助声发射技术全程检测了FSW接头疲劳过程中的声发射信号特点，给出了疲劳损伤的早期失效特征；研究揭示了决定铝合金搅拌摩擦焊接头抗腐蚀性能的特征第二相，阐明了接头的腐蚀失效机理，并建立了预腐蚀与超高周疲劳失效的联系。项目研究成果进一步丰富了焊接接头的超高周疲劳断裂理论，并为高速列车的抗疲劳设计和可靠性评定提供了理论基础。