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.