Microstructure and elemental analysis of ZnO-coated AZ91D magnesium alloy via anodic oxidation coating for corrosion protection

The AZ91D Magnesium alloy is a highly demanded structural material, valued for its exceptional mechanical and physical properties. Its versatility has led to widespread applications in industries such as automotive, aerospace, electronics, and biomedical. However, a significant limitation of AZ91D alloy is its poor corrosion resistance, which hinders broader adoption despite its advantages. To mitigate this weakness, surface treatments are essential to improve its corrosion protection. Among the various methods, anodizing stands out due to its low operational cost, short processing time, and straightforward setup. This research investigates the effect of coating time on the quality of anodic oxidation coatings with zinc oxide (ZnO) on AZ91D Magnesium alloy. The surface morphology, structural characteristics, and corrosion resistance of the ZnO-coated alloy were analyzed using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and corrosion testing. The findings demonstrate that anodizing effectively increased the thickness of the ZnO oxide layer on the AZ91D Magnesium alloy, significantly improving its corrosion resistance. Notably, the coating thickness increased proportionally with the duration of coating time. The sample with a 3-minute coating time exhibited the lowest corrosion rate of 2.17 mm/year, alongside the best coating quality, as confirmed by SEM, EDX, and XRD analysis. These results indicate that the elemental composition and compactness of the coating layer play a critical role in enhancing corrosion resistance.