Low Cycle Fatigue Behaviour of Extruded AZ61 and AZ80 Magnesium Alloys

Abstract

Extruded magnesium alloy shows a mechanical anisotropy caused by the particular deformation characteristics of the hexagonal crystal structure. Cyclic deformation behavior and fatigue life of the extruded AZ61 and AZ80 alloys were investigated in the total strain controlled low-cycle fatigue test in ambient atmosphere at room temperature. The low-cycle fatigue lifetime of the two alloys extruded was almost same, but AZ80 alloy treated by an artificial aging after the extrusion had shorter lifetime compared with the extruded alloy, even though higher static mechanical properties with the aging. The hysteresis loop in experiments showed asymmetric behavior in tension and in compression and differed from the hysteresis of steels et al. The particular shape of the hysteresis was caused by the difference of the yield stress between tension and compression, and pseudoelastic behavior during reloading in the opposite direction, which tends to be more pronounced in compression than in tension. The pseudoelastic strain of the aged specimen was smaller than that of the extruded specimen. It was suggested that the asymmetric phenomenon was revealed by the reversal of twins upon unloading and the fatigue fracture was affected by the formation of the twin.