拉-拉载荷下2195-T8铝锂合金在N2O4中的预腐蚀疲劳研究

Pre-corrosion Fatigue Performance of 2195-T8 Al-Li Alloyin N2O4Under Tension-Tension Load

摘要:

液体导弹在长期加注贮存的状态下,弹体与贮箱结构常因腐蚀损伤从而导致疲劳裂纹的产生乃至断裂等问题。采用疲劳寿命测试、扫描电镜以及能谱分析等方法,研究了2195-T8铝锂合金在N₂O₄中预腐蚀180天后的疲劳裂纹萌生、扩展和断裂机理,并与未腐蚀试样进行对比。结果表明：两种环境下试样的疲劳极限为145Mpa、118Mpa,循环应力降低比值约为18.62%；试样在预腐蚀的过程中,由于形成“闭塞区”,同时与富铜相粒子形成原电池,进一步加速腐蚀历程,形成多源裂纹萌生的特征,且更易从非金属夹杂区域起裂；受到晶粒间的位错、堆积等因素的影响,发现了垂直于疲劳辉纹、穿越大晶粒及途经小角度晶界的二次裂纹；两种环境中的疲劳瞬断区的断口形貌呈现出典型的沿晶韧窝和韧性断裂的特征。

Abstract:

In the state of long-term filling and storage of liquid missiles, the body and tank structure are often damaged by corrosion, which leads to fatigue cracks and even fractures. Fatigue life testing, scanning electron microscopy and energy spectrum analysis were used to study the fatigue crack initiation, propagation and fracture mechanism of 2195-T8 aluminum-lithium alloy pre-corroded in N₂O₄ for 180 days, and compared with uncorroded samples. The results show that the fatigue limits of the specimens tested in the two environments are 145Mpa and 118Mpa, and the cyclic stress reduction ratio is about 18.62%. During the pre-corrosion process, the sample forms an "occlusion zone" and forms a galvanic cell with the copper-rich phase particles at the same time, which further accelerates the corrosion process and forms the characteristics of multi-source crack initiation, and it is easier to crack from the non-metallic inclusion area. Affected by factors such as dislocation and accumulation between grains, it is found that it is perpendicular to the fatigue striations, passing through large grains, and passing through small-angle grain boundaries. The fracture morphology of the fatigue transient fracture zone in the two environments shows the characteristics of typical along-crystalline dimples and ductile fracture.