Influence of microstructural discontinuities on the behaviour of long cracks in the VHCF regime for the aluminium alloys EN AW 6082 and EN AW 5083
Influence of microstructural discontinuities on the behaviour of long cracks in the VHCF regime for the aluminium alloys EN AW 6082 and EN AW 5083
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微观结构不连续性对铝合金 EN AW 6082 和 EN AW 5083 VHCF 状态下长裂纹行为的影响
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
M. Zimmermann
中科院分区：
文献类型：
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作者：
T. Kirsten;F. Bülbül;M. Wicke;H. Christ;A. Brückner;M. Zimmermann
本文研究了两种不同的铝合金，沉淀硬化合金EN AW 6082(峰值时效和过时效)和加工硬化合金EN AW 5083(软退火态)。疲劳裂纹的萌生是通过聚焦离子束缺口来实现的，并用远距离显微镜对裂纹扩展行为进行了原位观察。研究了门槛值区附近恒定应力强度因子下的裂纹扩展。在现场调查过程中，发现了裂纹扩展速度的变化。可以观察到，尽管裂纹处于长裂纹扩展区域，但晶界和初生析出物的阻挡作用是导致裂纹扩展迟缓的主要原因。随着ΔK值的减小，显微组织的影响变得更加重要，同时平均裂纹扩展速率也随之降低。实验结果表明，铁基析出物对两种铝合金的裂纹扩展速率都有影响。同时，晶界导致裂纹扩展速度减慢，主要是在加工硬化铝合金的情况下。这被认为是EN AW5083的平均裂纹扩展速率比采用可比较的ΔK值时所观察到的沉淀硬化合金的平均裂纹扩展速率小的原因。
In the present study two different aluminium alloys, the precipitation hardening alloy EN AW 6082 (peak-aged and overaged) and the work-hardening alloy EN AW 5083 (soft annealed) were examined. Fatigue cracks were initiated by means of a focused ion beam notch and a longdistance microscope was used for in-situ observation of the crack growth behaviour. The crack growth was investigated at constant stress intensity factors near the threshold regime. During the insitu investigation a change in crack growth velocity was detected. It could be observed that the barrier function of grain boundaries and primary precipitations are the major reason for crack growth retardation despite the fact that the crack is in the long crack growth range. The microstructural influence becomes more important with decreasing ΔK values, meanwhile the average crack growth rate decreases simultaneously. Experimental results have shown that the Febased precipitates are influencing the crack growth rate for both aluminium alloys. Meanwhile, grain boundaries are causing a deceleration of the crack growth rate primarily in case of the work hardened aluminium alloy. This is assumed to be the reason for the smaller average crack growth rate in EN AW 5083 compared to that observed for the precipitation hardening alloy while applying comparable ΔK values.