Effect of anodized layer thickness on fatigue behavior of magnesium alloy

The process of anodizing has been adopted as an effective way to protect underlying material from corrosive environments. In the present study, since the corrosion protection ability would depend on thickness and quality of the anodized layer, effect of anodized layer thickness on fatigue behavior of AM60 magnesium alloy was investigated using three different anodized layer thicknesses of 15, 5 and 1 μm. The specimen with 15 μm thick anodized layer showed rough and irregular interface between substrate and anodized layer. Many defects were also observed in the anodized layer. But as the thickness of anodized layer was reduced from 15 to 5 to 1 μm, interface roughness was tended to be diminished. The role of interface roughness was reflected in the fatigue strength of three groups of specimens, where the specimen with the smoothest interface, 1 μm thick anodized specimen, showed the highest fatigue strength among the three groups. For the specimen with 15 μm thick anodized layer, the estimated value of ΔK at fatigue limit was almost equal to ΔKth (≈0.86 MPa√m) while for the specimens with 5 and 1 μm thick anodized layers the estimated ΔK values were well below the ΔKth, where the initial crack should be considered as small crack. Well-known Kitagawa–Takahashi diagram for the present three kinds of anodizing layer thickness suggested that the anodizing layer thickness would be preferred less than 5 μm.