マグネシウム合金AZ80展伸材のギガサイクル疲労挙動とフラクトグラフィ

概要

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In order to investigate the fatigue properties of extruded magnesium alloy in very high-cycle regime, rotary bending fatigue test was performed in ambient atmosphere at room temperature using the hourglass shaped specimens of AZ80 alloys extruded (F-specimen) and treated by an artificial aging after extrusion (T5-specimen). From the experimental results, there is no difference in fatigue lifetime between both specimens in the high stress amplitude level, but the T5-specimen had shorter lifetime compared with the F-spesimen in low stress amplitude and high number of cycles, even though higher static mechanical properties with the aging. Both specimens show a clear step-wise S-N curve on which two knees exist. Specific stress amplitude formed the knee corresponded to the yield stress of 160MPa in compression. It was concluded from the detailed observation of fracture surface that the step-wise S-N curve was induced by the crack initiation mechanism changing from the twin deformation in high stress amplitudes to slip deformation in low stress amplitudes, because of a mechanical anisotropy caused by the extrusion and the particular deformation characteristics of the hexagonal crystal structure in a magnesium alloy.
2009-06-25