On corrosion fatigue strength of the anodized and painted Mg alloy

• Effects of both anodized and painted surface-treatments on fatigue lives were minimal in air.
• Increases in the thickness of the anodized film lower the corrosion fatigue resistance.
• The load-induced strain within the painted film accelerates the liquid permeability of the film.
• Anodized-film thickness and roughness along the P/AD interface are key determining corrosion fatigue strength.

As an advantage of anodic oxide coating, both good wear resistance and high rigidity are expected due to its high surface hardness. However, unfortunately many narrow holes with different diameters are contained within the anodized coating. Therefore, it is very difficult for anodized coating to improve corrosion fatigue strength. So, the new hybrid method, i.e., anodic oxide coating plus painting treatment, was developed to increase corrosion fatigue strength of magnesium alloy. In the present study, fatigue tests were conducted on the extruded Mg alloy with different surface treatments in laboratory air and in the 3% sodium chloride solution. One is the anodized surface treated Mg specimens with different anodized film thicknesses. The other is the hybrid surface treated specimens, i.e., anodic oxide coating plus painting. In addition, the painted specimens without the anodized film were also tested. From the present study, it was considered that both the thickness of the anodized film and roughness at the interface between the painted and the anodized coating (P/AD) are key factors determining the corrosion fatigue resistance of the alloy. Effects of both the anodized and the painted surface treatments on the fatigue lives were minimal in laboratory air. However, in sodium chloride solution, increases in the thickness of the anodized film lower the corrosion fatigue resistance of the specimen. Corrosion fatigue lives of the painted specimens without the anodized film were not influenced by the corrosive environment.