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-SiO2 (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 Stober 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 similar to 153.4 degrees. 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 x 10(6) Omega 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.