Corrosion resistance and superhydrophobic properties of organic hybrid coating on cast Al–Si alloy

In this paper, a multiple hybrid coating (MHC) with good corrosion resistance and superhydrophobic property on the surface of cast Al–Si alloy was synthesized via a simple dip-coating method by using organosiloxane containing hydrophobic mullite-SiO 2 (M–S) particles as a precursor. The morphology, composition and water contact angle (WCA) of the coatings were investigated by SEM, FT-IR, XRD and OSA100, respectively. The results showed that the hydrophobic M–S particles was synthesized through modified Stöber method, which has a micro- and nano- scale structures. In addition, the morphology of the MHC presented that a dense and uniformly cover on the Al–Si alloy substrate formed a superhydrophobic surface with the WCA ∼153.4°. The corrosion protection of MHC was evaluated by using the Tafel polarization curves and electrochemical impedance spectroscopy. The coating with M–S particles exhibited much better corrosion resistance property than that of the untreated substrate and pure organosiloxane coating (OSC). The E corr was obviously more positive than that of them. Moreover, the corrosion current density of MHC was remarkably decreased by 5 and 3 orders of magnitude compared with other two coatings, respectively. The corrosion resistance of the MHC decreased gradually with increasing immersing time. However, the R ct value of MHC was still 2.31 × 10 6  Ω cm 2 after 168 h immersion testing in 0.6 M NaCl solution, which was nearly 322-fold higher than that of untreated substrate. Owing to the excellent superhydrophobic, corrosion resistance and long-term stability, the MHC possesses potential application in corrosion resistance of cast Al–Si alloy.