Architectural optimization of an epoxy-based hybrid sol–gel coating for the corrosion protection of a cast Elektron21 magnesium alloy

Abstract

An epoxy-based hybrid sol–gel coating was prepared in various architectural configurations has beenstudied for the corrosion protection of a cast Elektron21 magnesium alloy. The creation of a single layerof this coating presents defects consisting of macro-pores and protuberances, which opens access for cor-rosive species to reach the metallic substrate. These defects are suspected to result from the high reactivityof the substrate, as well as to the irregular topography of the substrate disrupted by the microstructureof the own magnesium alloy. Hence, a sol–gel coating in bilayer architecture is proposed, where the firstlayer would “inert” the surface of the magnesium substrate, and the second layer would cover the defectsof the first layer and also thickening the coating. The morphological characteristics of the sol–gel coatingswere analyzed by scanning electron microscopy (SEM), and their corrosion behavior was evaluated byOCP (open circuit potential) monitoring and electrochemical impedance spectroscopy (EIS) in chloridemedia. It is shown that both the architectural arrangement and the individual thickness of the first andsecond layers have an important influence on the anticorrosion performances of the protective system,just as much as its global thickness.