Al-Zn-Mg合金拉扭复合微动疲劳行为及其微观机理研究

Due to fretting fatigue widely exists in the key components of high speed train, tension-compression and combined axial torsional fretting fatigue tests are systematically performed for Al-Zn-Mg alloy which is one of the main materials used for high speed train, the change of dislocation configuration of Al-Zn-Mg alloy is researched. Fretting fatigue test apparatus with point contact is set up to realize tension-compression and combined axial torsional fretting fatigue, ANSYS finite element analysis is used to analyze stress distribution by numerical study using 2D and 3D finite element method, fretting fatigue characteristic and lives of Al-Zn-Mg alloy are intensively analyzed. Based on finite element analysis, macroscopic and microscopic experiments with tribology and fatigue research methods, fretting regions morphology and fretting fatigue fracture behavior are analyzed to realize fretting fatigue characteristic and mechanism, competitive relation between fretting corrosion and fatigue are discussed. The second phases of Al-Zn-Mg alloy due to fretting effect have a certain impact on the fretting fatigue properties so that the microstructure of material significantly affects fracture behavior. Fretting fatigue behavior and microstructure mechanism are investigated. Research on Al-Zn-Mg alloy combined axial torsional fretting fatigue properties and microscopic mechanisms can be to improve the level of application of the key components of high-speed train aluminum alloy materials, evaluation methods and techniques, as well as its security significance.

由高速列车关键部件普遍存在的微动疲劳问题，对高速列车关键材料之一的Al-Zn-Mg合金进行系统的拉压微动疲劳和拉扭复合微动疲劳试验，对其在微动疲劳过程中的细微观结构进行观察。通过设计点接触条件下的微动疲劳试验装置实现拉压和拉扭复合微动疲劳，对其进行建模与接触力学数值模拟，分析应力幅值对材料的拉压和拉扭复合微动疲劳特性及寿命的影响。在数值模拟、宏观试验和微观试验结果相结合的基础上，综合运用摩擦学和疲劳的研究方法，研究拉压和拉扭复合微动疲劳失效的特点及其机制，揭示在微动疲劳过程中微动磨损和疲劳的竞争关系；研究Al-Zn-Mg合金中的第二相与材料微动疲劳裂纹萌生与裂纹扩展的关系；建立材料的微观组织演变规律及微动疲劳损伤的微观机制。Al-Zn-Mg合金拉扭复合微动疲劳特性及其微观机理的研究，为提高我国高速高速列车关键部件铝合金的应用水平，建立材料的评价方法和技术，以及其安全使用具有重要的意义。

由高速列车关键部件普遍存在的微动疲劳问题，对高速列车主要材料之一的Al-Zn-Mg合金进行系统的拉压微动疲劳和拉扭复合微动疲劳试验，对Al-Zn-Mg合金在微动疲劳过程中的微观结构进行观察。通过设计点接触条件下的微动疲劳试验装置实现拉压和拉扭复合微动疲劳，对其进行建模与接触力学数值模拟，分析接触应力、应力幅值和频率对材料的拉压和拉扭复合微动疲劳特性及寿命的影响。结果表明在Al-Zn-Mg合金拉压微动疲劳和拉扭复合微动疲劳中，循环软化的程度随着应力幅值的提高增加；循环软化的所需的微动疲劳周期随着接触应力的提高缩短；Al-Zn-Mg合金拉压微动疲劳和拉扭复合微动疲劳寿命远低于在相同条件下不承受接触应力的纯疲劳寿命并随接触应力、应力幅值和频率的增加而降低。通过数值模拟计算，对于Al-Zn-Mg合金拉压微动疲劳，接触面均存在粘着区、滑动区和张开区且随应力幅值或者接触应力的变化而改变。根据Al-Zn-Mg合金微动损伤过程中微动斑形貌特征，可以将微动区域划分为部分滑移区、滑移区以及混合区，微动疲劳断裂过程包括裂纹萌生、裂纹扩展到断裂。微动疲劳裂纹萌生源为试样和微动桥接触处的微动磨损处，材料特性与微动疲劳因素影响微动疲劳裂纹的扩展方式。位错结构和位错密度在循环加载过程中会发生变化，由于位错的交互作用导致在这些区域产生应变集中而使塑性变形受阻从而使微裂纹形核，材料的微结构显著影响材料的断裂行为。