LC4CZ铝合金机场环境下点蚀萌生疲劳裂纹行为研究

Research on Pitting Corrosion Nucleating Fatigue Crack Behavior of LC4CZ Aluminum Alloys inAirport Environment

关键词:  铝合金  机场环境  点蚀  疲劳裂纹  裂纹萌生  疲劳寿命分析

Key words:  Aluminum alloys  Airport environment  Pitting corrosion  Fatigue crack  Crack nucleation  Fatigue life analysis

摘要:

为获取LC4CZ铝合金机场环境下点蚀损伤萌生疲劳裂纹行为规律，开展了LC4CZ试件模拟机场环境、点蚀周期分别为10y和15y的加速点蚀试验，在此基础上进行预点蚀试件常幅载荷条件下分阶段疲劳试验，采用扫描电镜对分阶段试件断口进行观测并进行统计分析。研究发现，点蚀损伤程度对试件疲劳寿命有较大影响，两种点蚀周期下的疲劳寿命降低系数分别为4.3和5.8。30个预点蚀试件断口观测到的147条疲劳裂纹全部由蚀坑萌生，大都位于蚀坑底部且萌生周期短暂。两种腐蚀周期下的疲劳裂纹萌生初期的平均尺寸分别为21μm和33μm，在尺寸上属于短裂纹。随着疲劳循环数增加，两种点蚀周期下观测到的裂纹数量分别由21条和27条减少为15条和24条，多个裂纹之间存在干涉、合并行为。

Abstract:

In order to obtain the behavior rule of LC4CZ aluminum alloy pitting corrosion damage nucleating fatigue cracks in airport environment， the accelerated pitting corrosion test according to test spectrum which simulated the airport environment was carried out， the corrosion period was respectively 10 and 15 equivalent corrosion year， after pitting corrosion test， the different interrupted period fatigue test of pre-corrode LC4CZ specimen under constant amplitude load was followed， then a subsequent fracture surface images photoed by scanning electron microscope was observed and the observation results were statistically analyzed. Based on the tests and the observation results， it is deduced that the corrosion damage has great reductive effect on the fatigue life， the reduction factor under 10 and 15 equivalent corrosion year respectively is 4.3 and 5.8; 147 fatigue cracks are observed from 30 specimen fracture surface which all initiate from corrosion pits and most of them locate at the bottom of pits with little locating at the pits side， and the crack initiation behavior is immediate upon the application of cyclic loading. From the point of crack size， the average crack length under two typical corrosion year respectively is 21μm and 33μm， so the pit-nucleated cracks are the small crack， and the number of cracks under two typical corrosion year respectively decreases from 21 and 27 to 15 and 24 with the loading cycle increasing， there is behavior of interrupting and coalescing between multiple fatigue cracks.