Effect of the eutectic phase mixture on the anodic behavior of alloy AZ91

The anodic behavior of magnesium–aluminum–zinc Alloy AZ91 was investigated in H3PO4 buffered solutions at pH 7 and 11 in the presence and absence of Cl− ions using a potentiodynamic polarization technique. In order to observe better the individual effects of the microstructural constituents on the corrosion behavior of AZ91, the polarization characteristics of the pure Mg, pure Al, AZ21 and AZ501 were also analyzed. Whereas, the eutectic phase mixture in AZ91 was an effective anodic barrier at pH 7, it was preferentially attacked region of the alloy at pH 11. The presence of Cl− ions resulted in localized attacks in the microstructure and as the concentration of Cl− ions increased, the severity of the localized attacks also increased at both pH 7 and 11. It was also observed that the significance of the influence of high amount of Cl− ions on the polarization behavior of different microstructural constituents was not same at pH 11.