Correlative evaluation of the corrosion resilience and passivation properties of zinc and aluminum alloys in neutral chloride and acid-chloride solutions

Abstract

Comparative analysis of the corrosion resilience and passivation characteristics of pure zinc (Zn) and aluminum (Al) alloys in neutral chloride and acid-chloride solutions at 0.5–3% NaCl concentrations was done with potentiodynamic polarization, potentiostatic evaluation, optical characterization, and open circuit potential measurement. Results show Al alloy was more resistant to general corrosion in both solutions with values ranging from 0.031 to 0.082 mm/year, and 0.037 to 0.389 mm/year compared to Zn alloys with values of 0.432–0.691 mm/year and 0.465–5.016 mm/year. Corrosion potential values of Zn alloy were significantly more electronegative than the values for Al alloy. The passivated region of the polarization plots for Al was thermodynamically unstable with visible current transients compared to that of Zn. Passivation of Al occurred at the early onset of anodic polarization in the neutral chloride solution. Zn alloy passivated at specific potentials, coupled with stable passivation behavior. The passivation range values of Al were generally greater than the values for Zn due to delayed stable pitting activity. Optical images for Al showed extensive localized degradation along specific regions and grain boundaries, whereas Zn morphology indicates general surface degradation. Open circuit potential plots indicate significant growth of Al2O3 oxide on Al coupled with active–passive transition behavior of the oxide. This contrasts the observation for Zn where the plot configuration indicates limited oxide formation and growth but significant thermodynamic stability.

Keywords

• corrosion
• passivation
• aluminum
• zinc
• pitting