Under Film/Coating Corrosion

Two principal under-film/coating corrosion phenomena, namely cathodic delamination and filiform corrosion, are discussed in detail. Historical contributions to the field are briefly reviewed but emphasis is given to the latest research findings. The various mechanisms by which corrosion causes organic coatings to disbond from a metal surface are examined with regard to which of these will be important for particular coated systems. The role of pretreatments, corrosion inhibitors, and alloying of the metal surface in reducing underfilm corrosion rates are discussed in relation to these mechanisms. Finally, the protective application of electrically conducting polymers, such as polyaniline, is critically reviewe

Initial stages of localized corrosion at cut-edges of adhesively bonded Zn and Zn-Al-Mg galvanized steel

The mechanisms of the initial stages of localized corrosion at cut edges were investigated for adhesively bonded Zn (Z) and Zn-Al-Mg (ZM) galvanized steel. The results provided strong evidence for the localized nature of corrosion of galvanized coatings at the cut edges and at the adhesive/zinc interface. In both cases a defined localized corrosion attack on zinc in Z sample was observed. On the contrary, in the case of the ZM specimen both zinc solid solution and eutectics exhibited local corrosion. The local attack at the adhesive/Z(ZM) interface was correlated with an anodic undermining process. It develops near the cut-edge surface and at the buried deep adhesive-zinc interface and results in adhesive disbonding in the buried interface. The electrochemical studies revealed that the corrosion kinetics at the metal cut-edges decreases during immersion, which could be due to formation of corrosion products on both steel and zinc surfaces. (C) 2016 Elsevier Ltd. All rights reserved