The formation of optical dark area (ODA) on high-cycle fatigue fracture surface of Al alloys at atmosphere is very common and questionable in the engineering fields. Herein, we discovered that the oxygen induced inner friction causes the serious Cu element segregation in the form of nanoparticles on the fatigue fracture surface at atmosphere, which forms the ODA in Al–Cu–Mg alloy. By increasing stress ratio or applying Vaseline coatings fatigue tests, the ODA can be absolutely eliminated simultaneously with a significant extension of their fatigue lives.

中文翻译：

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内摩擦引起的大气中Al-Cu-Mg合金高周疲劳断裂面的光学暗区（ODA）的形成

在大气中铝合金的高周疲劳断裂面上形成光学暗区（ODA）在工程领域中是非常普遍且值得商question的。在这里，我们发现氧气引起的内摩擦导致大气中疲劳断裂表面上的纳米颗粒形式的严重的Cu元素偏析，从而在Al-Cu-Mg合金中形成ODA。通过增加应力比或应用凡士林涂层进行疲劳测试，可以绝对消除ODA，同时显着延长其疲劳寿命。