Corrosion resistance and superhydrophobicity of one-step polypropylene coating on anodized AZ31 Mg alloy

Superhydrophobic coatings have been considerably used in corrosion and its protection of metallic Mg. And the comprehensive performance (hydrophobicity, bonding strength, and corrosion resistance, etc.) of the top coating may be highly dependent on the physical and chemical properties of the primer or under coat. Herein, an integrated superhydrophobic polypropylene (PP) coating was fabricated on the micro-arc oxidized Mg substrate via one-step dipping. Surface morphologies and chemical compositions of the composite coating were examined through Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and field-emission scanning electron microscopy (FE-SEM) together with X-ray photoelectron spectroscopy (XPS). The surface wettability of the coating was determined by contact angle and sliding angle. The corrosion-resistant performance was evaluated via electrochemical and immersion measurements. The results showed that the hybrid coating possessed micron-scaled granular structure on the surface with a high water contact angle of 167.2 ± 0.8° and a low water sliding angle of 2.7 ± 0.5°. The corrosion resistance of superhydrophobic coating was obviously enhanced with a low corrosion current density of 8.76 × 10−9 A/cm2, and the coating still maintained integrity after 248 h of immersion in 3.5 wt% NaCl aqueous solution. The MAO coating provides better adhesion of PP to the surface. Hence, the superhydrophobic coating exhibited superior bonding strength, corrosion resistance and durability.