Corrosion mechanisms and protection of Zn-Mg coatings applied on steel

摘要

Due to its high corrosion resistance, zinc coated steel is largely used in wide range of industriessuch as household appliances, construction or automotive. However, the sensitivity of zinc toaggressive environments, the intensive consumption of zinc and the increase in coating price areso many factors that are limiting the use of zinc coatings. A lot of coatings formulations haveconsequently been studied for many years in order to reduce the consumption of zinc and its costin coatings. The addition of magnesium into the metallic coating was proved to improve corrosionresistance in atmospheric conditions without increasing thickness [1]. However, there is a lack ofinformation about the behavior of Zn-Mg coatings in immersion, namely in the case of waterretention inside hollow bodies. Moreover, the high dissolution rate of magnesium due to its highelectronegativity is a critical parameter that affects the corrosion mechanism of the coating. Thus,the study focused on the in-depth understanding of the dissolution process, in order to develop ananti-corrosion system considering the complex behavior of the substrate.Three axes were developed in order to achieve this aim. On a first part, the surface corrosion andthe sacrificial protection mechanism were studied at both global and local scales [2,3]. On asecond part, the efficiency of corrosion inhibitors was investigated by means of electrochemical,analytical and surface analysis techniques in order to reduce the dissolution rate of the substrate inimmersion conditions. Benzotriazole (BTAH) was found to be the most effective molecule and itsinhibition mechanism in chloride solution was analyzed in details [4]. By regarding the dissolutionand inhibition protection mechanism of Zn-Mg coated steel, a coating with BTAH-layered doublehydroxide was developed and its efficiency was discussed.