Corrosion resistance of fatty acid and fluoroalkylsilane-modified hydrophobic Mg-Al LDH films on anodized magnesium alloy

Super-hydrophobic films were synthesized on the Mg alloy AZ31 by modifying in-situ grown Mg-Al layered double hydroxide (LDH) films with stearic acid (SA), sodium laurate (SL), myristic acid (MA) and 1H, 1H, 2H, 2H–perfluorodecyltrimethoxysilane (PFDTMS). These films exhibited a static water contact angle of 150.6°, 153.7°, 152° and 145.5°, respectively. Mg-Al LDH-SA, Mg-Al LDH-SL and Mg-Al LDH-MA films were produced by the neutralization reaction of the fatty acid and Mg(OH)2 whereas the Mg-Al LDH-PFDTMS film was produced by the hydrolysis reaction of PFDTMS along with the condensation polymerization reaction. The electrochemical impedance spectroscopy (EIS), the hydrogen evolution data as well as long-term immersion tests indicated that Mg-Al LDH-PFDTMS provided better barrier protection to improve the corrosion resistance of AZ31 Mg compared with the Mg-Al LDH-SA, Mg-Al LDH-SL and Mg-Al LDH-MA films, because the SiOH groups and the hydroxyl groups on the surface of the film were combined to form CF3(CF2)7(CH2)2Si(O-Surface)3, which decreased the surface energy and improved the corrosion resistance.