The effect of pre-anodizing on corrosion behavior of silicate conversion coating on AA2024

Potassium silicate was deposited on anodized AA2024 aluminum as conversion coatings. The corrosion behavior of the coatings was examined by means of electrochemical impedance spectroscopy, potentiodynamic polarization and surfaces techniques. Potentiodynamic polarization curves show significant decrease in corrosion current density of silicate coated aluminum in NaCl solution. Anodizing shows significant effect in silicate conversion coating and the corrosion resistance was increased with increasing anodizing time. The coating obtained from a higher concentration of silicate solution leads to a very thick film, which may cause the formation of pores on the surface. The results indicated that the coating applied from 1 M silicate baths on 1200 s anodized aluminum is more uniform and continuous and high corrosion protection was obtained. The coating performance was evaluated in acidic and basic NaCI solution and the results show the stability of silicate conversion coating in these solutions. (C) 2014 Elsevier B.V. All rights reserved.