4046 Effect of anodized layer on fatigue mechanism of magnesium alloy

概要

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Anodic coatings generally degrade the stress-life (S-N) fatigue performance of a material. So far many research works have been carried out on the effect of anodic coating on fatigue performance but very few of them deal with the possible effect of anodizing thickness on the fatigue behavior. Hence, rotating bending fatigue test was conducted in laboratory air under the stress ratio, R, of 0.1 using smooth specimen with anodized film thickness of 15 and 5μm. Fatigue strength of anodized specimen decreased considerably as compared with that of the untreated one. But the degradation of fatigue life was much more pronounced in 15μm coating compared to the 5μm coated samples. It was pointed out through study that the fatigue strength of anodized alloy was controlled by the crack initiation behavior in the coating and the result of the interrupted fatigue test showed a much faster crack initiation time in anodized materials compared with that of the base metal. Crack imitation time increased with decreasing coating thickness causing an improvement in fatigue behavior. Fractographic observation also revealed the presence of many flaws in 15μm coating compared to that of the 5μm one that also lead to better fatigue performance of the later under low humidity condition.
2006-09-15