Corrosion resistance of a superhydrophobic surface on micro-arc oxidation coated Mg-Li-Ca alloy

•A superhydrophobic surface was fabricated on Mg-1Li-1Ca alloy with SA.•SA can infiltrate into the micropores of the MAOand react with substrate.•The MAO is sealed with SA and MgSt to block the penetration of aggressive ions.•SA coating peels off due to its dissolution, and the stress caused by corrosion.

A superhydrophobic surface was successfully fabricated on micro-arc oxidation (MAO) coating on Mg-1Li-1Ca magnesium alloy via surface modification with stearic acid (SA). The microstructure, composition and superhydrophobic characteristics of the MAO/SA composite coatings were investigated by means of SEM, EDS, XRD, XPS, FT-IR, and contact angle (CA). The corrosion resistance of the coatings was assessed by potentiodynamic polarization, electrochemical impedance spectrum (EIS), and immersion test in 3.5 wt % NaCl solution. The results demonstrated that the morphology of the porous MAO surface was transformed to a novel petal-like clusters after modified with SA. The magnesium stearate and SA were deposited in/on the micro-pores and the surface of the MAO coating. The CA of the SA-modified surface reached 155.5°. The corrosion current density of the MAO/SA-7h coating decreased about three orders of the magnitude compared to the substrate. The SA-modified surface can provide a long-term corrosion protection for the Mg-1Li-1Ca alloy. Additionally, the coating formation mechanism as well as the corrosion mechanism were proposed and discussed.