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The plate bending fatigue tests with stress ratio of -1 and 0 were conducted for the Mg-9mass%Al-1mass%Zn-2mass%Ca extruded plates, MIG joints and TIG joints. Fatigue limit of the plates along the extruded direction (ED) was smaller than that of the plates along the transverse direction (TD) for each stress ratio. It is likely that the anisotropy was attributed to the spread of basal pole in the ED and the rotation of basal pole toward the TD. Fracture occurred at the center of the specimens of MIG and TIG joints, and fatigue limits of both joints were lower than that of the extruded plates. Fatigue limit of TIG joints, however, was about 50 to 60% of MIG joints. SEM observations indicated that fatigue cracks initiated at the second phase particles (Al-Ca compounds) and propagated near them. Fracture occurred as a result of the crack connection. The size of the second phase particles in TIG joints was larger than that in MIG joints, so that the crack length was larger in TIG joints. It is likely that the larger size of the second phase particles was attributed to the lower fatigue limit of TIG joints.

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