Abstract
Plane bending fatigue test had been conducted to investigate fatigue crack initiation mechanism in coarse-grained magnesium alloy, AZ31, under different mean stress. The initial crystallographic structure was analyzed by an electron backscatter diffraction (EBSD) method. When the test had been conducted at the load ratio R=-1, secondary twin operated in a primary twin and resulted in the fatigue crack initiation. On the other hand at R=0.1, dual twin was activated and crack has initiated along the grain boundary.
