Abstract
In order to investigate the high cycle fatigue properties, the fatigue crack initiation property and the small fatigue crack propagation behavior of AZ31 extruded magnesium alloy, rotating bending fatigue test were carried out in air at room temperature. And fatigue crack observation with replication technique were also carried out. As the results, it was cleared that the fatigue crack initiation sites were the inclusions at surface and the fatigue crack propagated through grain boundaries.