Corrosion performance of composite galvanic coatings with variable concentration of polymeric nano-aggregates and/or Cr(III) conversion layers

This paper reports on the corrosion performance of composite zinc layers (similar to 8 mu m) on a steel substrate, considering the influence of nano-aggregates and Cr(III) conversion layers, compared to control (only Zn layers) conditions. The main factors, influencing the corrosion performance of Zn in this study are: a) the effect of two concentrations of polymeric nano-aggregates (0.1g/l and 0.3g/l PEO113-b-PS218 core-shell micelles in the starting electrolyte); b) the effect of Cr(III) conversion layers on both pure Zn and composite Zn layers. For most of the hereby investigated time intervals i.e. treatment in aerated 5% NaCl from 2h until 120h, the composite coatings present higher corrosion resistance, especially within longer treatment. Corrosion current densities are similar to Zn, however, anodic currents are significantly lower. After treatment in NaCl, the composite Zn coatings present a more homogenous product layer, formed as a result of the presence of the nano-aggregates. The additional Cr(III) treatment does not significantly improve the corrosion resistance of the composite coatings for the hereby investigated time intervals.