In-situ growth and anticorrosion mechanism of a bilayer CaCO3/MgO coating via rapid electrochemical deposition on AZ41 Mg alloy concrete formwork

An anticorrosive CaCO3/MgO coating was obtained on AZ41 Mg alloy via rapid electrochemical deposition for the application of concrete formwork. Surface characterization was carried out to obtain the morphology and chemical composition of the coating. Afterwards, long-term anticorrosion performance was investigated via electrochemical methods in the chloride-containing Portland cement system. Results show that the electrochemical deposited coating consists of an outer CaCO3 layer and a compact inner MgO layer. Pre-immersion in the electrochemical deposition electrolyte contributed to the formation of a dense coating. The pretreatment plays an active role in the formation of an inner MgO layer, which significantly enhanced the binding between outer CaCO3 layer and Mg substrate. The electrochemical deposited CaCO3/MgO coating with pretreatment shows improved anticorrosion property than the coating without pretreatment, which could be ascribed to the formation of the dual-layer structure. Additionally, corrosion mechanism is suggested and discussed for the CaCO3/MgO coating.