Abstract
Reversed plane bending fatigue tests were conducted for two kinds of fine-grained Aluminium alloys (Nano aluminium) different in micro structures. The effect of specimen collection orientation was also investigated using totaly four kinds of specimens. Initiation and initial growth behavior of small fatigue crack were observed by means of plastic replicas technics. It was found that either inclusions or weak boundary between powders were responsible for fatigue crack initiation depending on the materials. Hardly any difference was found in crack growth behavior among those materials.