FATIGUE BEHAVIOUR OFA ROLLED AZ۳۱ MAGNESIUM ALLOYS PREPARED BY EPAND BB CONDITIONS

Abstract: Rotating bending fatigue tests have been performed using smooth specimens of a rolled AZ۳۱ magnesium alloy in laboratory air at ambient temperature. Fatigue strength and characteristic was evaluated and fracture mechanism was discussed on the basis fracture surface analysis. Electrical polishing (EP) as well as deep rolling (ball burnishing (BB)) U-notched specimens were performed on two groups of samples, to evaluate optimum conditions for fatigue life. The microstructure and tensile properties of roll cast (RC) Mg- ۳% Al- ۱% Zn (AZ۳۱) was investigated. The fatigue strength of ۱۰۷ cycles around ۱۰۰ MPa for deep rolling while it was around ۴۰ MPa for Electrical polishing. It was very important to understand the effect of (ball burnishing (BB)) conditions on the hardness of the surface through to the core. The two procedures improved the fatigue performance, but better improve in results were found in ball burnishing. The growth of small cracks initiated at the surface coincided with the FCP characteristic after allowing for crack closure for large cracks, but the operative fracture mechanisms were different between small and large cracks. At the subsurface crack initiation site, smooth facets were always present regardless of applied stress level.

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Keywords: AZ۳۱ , Fatigue , Surface treatment , Ball burnishing , Electrical Polishing.