城轨车辆用某型铝合金框架结构失效分析

Failure Analysis of an Al-Zn-Mg Alloy Based Frame Structure of Urban Rail Vehicles

本文针对城轨车辆用某型7XXX系铝合金框架结构出现的裂纹问题,采用光学金相、扫描电镜、透射电镜等表征手段进行了失效分析,探明了结构故障的原因,同时结合有限元分析揭示了材料的失效机理。结果表明,本文所述铝合金框架结构故障类型为环境腐蚀和疲劳耦合作用引起的开裂。其主要微观机理在于,材料本身晶界析出相呈连续分布,耐蚀性能不足,在焊接热影响下,容易使得材料形成晶内析出相数量减少,晶界连续分布着粗大析出相的组织特征,从而容易在腐蚀环境和疲劳载荷的作用下产生失效;有限元分析结果表明,该故障位置最低寿命约105.2次,约74万Km,与实际寿命基本吻合。

A crack incident of an Al-Zn-Mg alloy based frame structure of urban rail vehicles was investigated in this paper. Optical Metallography (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM) were conducted to the failure analysis. The mechanisms of the crack were revealed by joint results of microstructure analysis and finite ele-ment analysis. The results showed that the cracks on the frame structure were attributed to the coupling effects of environmental corrosion and fatigue. The exact failure mechanism was that the precipitated phase at the grain boundary of the material itself is continuously distributed, and the corrosion resistance is insufficient. On the effects of welding heat, it was easy to reduce the number of intragranular precipitated phase, and the precipitation on grain boundary was continuously dis-tributed with the structural characteristics of coarse precipitated phase, which is easy to cause fail-ure under the effect of corrosion environment and fatigue load. The results of finite element analy-sis showed that the minimum life of the cracking position is about 105.2 cycles, which tallies with the reality service life of the studied frame structure.