抄録
Fatigue crack initiation behavior of shot-peened magnesium alloy AZ31 was investigated. Fatigue tests were conducted using a rotary bending fatigue testing machine. The fatigue specimens were machined from two directions. Their loading directions are parallel and perpendicular to rolling direction. In the finite life regime, the shot peening improved the fatigue life significantly and the anisotropy in fatigue life disappeared by shot peening. On the other hand, fatigue limit of peened specimen was almost the same in comparison with that of untreated specimen. And the anisotropy in fatigue limit still remained. The crack initiation behaviors at stress amplitude of 115MPa were observed using an optical microscope. The small crack was initiated along the twin boundary at the early stage of fatigue life even in shot peened specimen. However, the crack growth was delayed by shot peening, resulting in the improvement of fatigue life in shot peened specimen.
