Recently, aluminum alloys have been applied to more structural parts of automobiles. In order to imove the reliability of the automobile furthenriore, it should be verified 1ether the stress concentration due to the scars influences on the fatigue strength. Fatigue test and stress simulation were carried out to obtain cpantitatively hemispherical pits effect on fatigue strength for extruded thick plates of 6000 series aluminum alloys. As the size effect of the pit, the relationship between strength reduction factor and volume of stress concentrated area was shown.
