Effect of Surface Texture and Humidity Environment on High Cycle Fatigue Property of Wrought Magnesium Alloys AZ31 and AZ61

Abstract

Rotating bending fatigue tests on AZ31 and AZ61 wrought magnesium alloys were carried out in order to investigate the effects of specimen surface texture and the humidity environment of experiment. Specimen surface texture was varied by using an emery paper of a different roughness or by buff polishing to mirrored surface in final finish of specimen surface treatment. The conditions of environment in which fatigue tests were conducted were the laboratory's air, the dry air, the humid air and the water. As a result, the fatigue life of a specimen with a rough surface was shorter than that with a smooth surface. But the fatigue life of a specimen with mirrored surface was shorter than that with a little rougher surface by an emery polishing. It is attributed to that the effect of work-hardened layer on the fatigue life exists. And then the fatigue life is predicted by the √area parameter model in which a depth of surface roughness is regarded as a size of defect. The effect of surface roughness was more apparent in the case that a specimen is polished in the circumferential direction which is parallel to the crack propagation direction compared with the case that a specimen is polished in the axial direction. The fatigue strength in the region of a long fatigue life in water was smaller than that in the other environments; however this feature is not so apparent in the region of the short life. Except for in the water environment, the fatigue life became shorter in the descending order of the dry air, the laboratory's air and the humid air.