Hydrophobic composite layers for enhancing long-term corrosion resistance of Al alloy micro-arc oxidation coating

To enhance the long-term corrosion resistance of the micro-arc oxidation (MAO) coating on Al alloys, sealing and hydrophobic modification of MAO coating were carried out in this study. Firstly, isophorone diisocyanate trimer (IPDI) and gamma-mercaptopropyltrimethoxysilane (MPTMS) were selected as assembly molecules to alternately assemble layer by layer on the MAO coating. Then SiO2 nanoparticles and 1H, 1H, 2H, 2H-perfluorodecyltrimethoxysilane (TMS) were introduced to the MPTMS/IPDI layer, and a hydrophobic composite coating (MAO-SiO2 TMS) was obtained. The MPTMS/IPDI layer reduced the surface defects and surface roughness and improved the corrosion resistance of the MAO coating. After introducing SiO2 particles and TMS into the MPTMS/IPDI layer, the surface roughness of the coating further decreased from 1.725 mu m to 1.1117 mu m. The contact angle of the MAO-SiO2-TMS coating reached the superhydrophobic level (150.61, which was higher than that of the MAOMPTMS/IPDI (85.31. In addition, the MAO-SiO2-TMS coating significantly enhanced the long-term corrosion protection of the MAO coating due to the outstanding sealing effect and hydrophobic stability. In particular, the vertical bar Z vertical bar(0.01Hz) and R-o of MAO-SiO2-TMS coating were up to 1.71 x 10(8) Omega.cm(2) and 2.56 x 10(6) Omega.cm(2) after 3336 h of exposure to 3.5 % NaCl solution, respectively. The MAO-SiO2-TMS coatings exhibited excellent long-term corrosion resistance in a corrosive environment due to their outstanding sealing effect and hydrophobic stability.