Corrosion characteristics of Alloy AZ63 in buffered neutral solutions

The polarization and electrochemical impedance spectroscopy techniques were used to analyze the corrosion behavior of Alloy AZ63 (6% Al and 3% Zn) in H3PO4/KOH buffered K2SO4 solution at pH 7. The presence of β phase resulted in formation of the deeper localized corrosion regions in as-cast AZ63. The oxide layer formed on homogenized AZ63 was estimated to be more continuous and protective. The middle frequency capacitive loop, which appeared at corrosion potential, in the impedance spectra arose from the relaxation of the mass transport of magnesium dissolution products in the solid oxide phase. Both the galvanic interactions between the micro-structural constituents and the stability of the partially protective oxide layer were estimated to control the corrosion characteristics of Alloy AZ63.