The fatigue crack propagation behavior of pure magnesium single crystals has been investigated in laboratory air at room temperature. Two types of CT specimens with different notch orientations were prepared from the magnesium single crystal made by the Bridgeman technique. Fatigue crack propagation behaviors of each specimen were different related to notch orientation. In the case of C-specimen with (1010)[0001] notch, a crack was inclined to (0001) gradually at low ΔK. To investigate crack propagation behavior along [0001], a tri-crystal specimen in which has (1010)[0001] notch was prepared. A crack propagated to [0001] in this specimen and the fatigue surface shows striation-like pattern. In the case of E-specimen with (0001)[1010] notch, a crack propagates parallel to basal plane. {1012} twin occurred in front the crack at higher ΔK level. A fatigue surface of the E-specimen was changed by {1012} twin formation.
