Orientation Dependence of Fatigue Behavior of Magnesium Single Crystals in Thin Sheet Plane Bending Method

Abstract

In this study, to clarify the orientation dependence of fatigue strength and fatigue life in magnesium, fatigue test of pure magnesium single crystals with different orientations have been performed by originally developed test method for small specimen. Moreover, Mg-Y alloy single crystals were tested to understand alloying effect to fatigue behavior of magnesium. In the A- and the B-specimen of pure magnesium, whose crack direction is normal to [0001] and crack plane is normal to (0001), a fatigue crack propagated [1100]. The cracks would be propagated due to alternating shear of secondary pyramidal slip. In the C and the D-specimen, whose crack direction is parallel to [0001], a fatigue crack propagated parallel to [0001] with activation of basal slip at the crack tip. In E-specimen, whose crack plane is parallel to (0001), a fatigue crack propagates (0001) and {1012} twin was formed around the crack tip. S-N plots showed strong orientation dependence. Fatigue life of C and D-specimen was longest and fatigue life of E-specimen was shortest among these five specimens. Fatigue crack in pure magnesium does not prefer to propagate twin interface so much. In the B-specimen of Mg - 0.75at.%Y alloy, a fatigue crack propagated [1100]. The crack behavior is similar to the case of pure magnesium. Fatigue file and fatigue limit were increased by yttrium addition.