Correlative evaluation of the corrosion resilience and passivation properties of zinc and aluminum alloys in neutral chloride and acid-chloride solutions
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Abstract
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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
TJ Mechanical engineering and machinery, TP Chemical technology