Cyclic Deformation and Fatigue Crack Behavior of Extruded AZ31B Magnesium Alloy

Pseudoelastic behaviors were observed in compressive and tensile loading-unloading tests at room temperature. The large anelastic strains were observed in compressive stress-strain hysteresis loops. The fatigue limit of axial load-controlled fatigue test at 107 cycles was 90MPa at room temperature. The deformation twins were observed in the specimen subjected to the higher stress amplitude of fatigue limit and free deformation twins were observed in the specimen subjected to the lower stress amplitude of fatigue limit. Stress-strain hysteresis loops were linear in tensile and compressive phases at the lower stress amplitude of fatigue limit and the complicated pseudoelastic deformations were observed in tensile and compressive phases at the higher stress amplitude of fatigue limit of axial load-controlled fatigue tests. Compressive mean strain generated by cyclic pseudoelastic deformations at the higher stress amplitude of fatigue limit. Fatigue cracks initiated at the secondary particle/matrix interface or broken secondary particle near the surface. Subsequently, small cracks tended to grow through transgranular.