Anti-corrosion Coating Of Az31 Magnesium Alloy Surface Preparation And Corrosion Resistance,

Polypyrrole (PPy) was chemically synthesized on the surface of the silane pretreated AZ31 magnesium alloy. Fourier transform infrared spectroscopy (FTIR) was used for structural characterization of the formed silane and PPy films. Scanning electron microscope (SEM) and energy dispersive X-ray (EDS) analysis were used for observation of surface morphology and elements analysis of the films. The corrosion behavior of silane film and PPy film was studied in 3.5wt% NaCl solution using electrochemical polarization test, electrochemical impedance spectroscopy and immersion test at room temperature.The corrosion behavior of AZ31 Mg pretreated with BTESPT and APS silane respectively was studied. The silane moleculars were cross-linked through SiOSi, and the silane film was linked to the Mg alloy by SiOMg. Silane pretreatment can improve the corrosion protection performance of AZ31 Mg alloy and a lower corrosion rate correlated with higher pH. Mg/APS played worse anti-corrosion performance than Mg/BTESPT because of hydrophilic NH2 group.The anti-corrosion performances of PPy films through different polymerization processes were investigated, including pretreatment, oxidant, reaction temperature and time. The PPy film showed a certain corrosion inhibition on the AZ31 magnesium alloy, with a decrease in the corrosion current density by one order of magnitude. Silane pretreatment can improve the corrosion protection performance of the Mg/PPy system, causing a positive shift of the corrosion potential by 110 mV and a decrease in the corrosion current density by two orders of magnitude. PPy using (NH4)2S2O8 as an oxidant showed better protection performance than FeCl3. Doped anion played a certain corrosion inhibition in Mg/APS/PPy system.10min was the best polymerization time of PPy using sodium dodecyl benzene sulfonate (SDBS) as a doping agent and (NH4)2S2O8 as an oxidant. And polymerization at temperature of 5～10℃was better than at room temperature.The mechanism on formation of PPy film was discussed. PPy was connected to the Mg alloy by physical adsorption, which induced the poor adhesion and continuity of PPy film, decreased its corrosion protection performance. After silane pretreatmen, silane film was linked to the Mg alloy by SiOMg, while linked to PPy by chemical bond, which enhanced the adhesion between PPy and Mg matrix, made the arrangment uniform and reduced the defects of PPy film.