Study On The Preparation And Performance Of Polypyrrole/Epoxy Composite Coating On Mg Alloy

Mg alloy is widely used in various fields for its outstanding performance. But it is liable to corrode which increases security risks in the process of using and reduces the service life.Mg alloy is coated by organic coating, which is one of the common surface modification technologies to improve corrosion resistance of Mg alloy. However the binding force between organic coating and magnesium alloy substrate is worse. The middle film—conducts polymer Polypyrrole, is used for improving the binding force between epoxy coating and Mg alloy in this paper. Firstly, the eigenstate polypyrrole film and Polypyrrle/Silane (PPy/Silane)composite film was prepared on the surface of Mg alloy, respectively. The effect of various factors on the corrosion resistance was researched. Then the corrosion resistance of organic coating which was coated with different pretreated was discussed.Eligenstate polyoyrrole film was electro-polymerized on the surface of Mg alloy by using cycle voltammetry, The effect of concentration of pyrrole monomer, cycle, scanning speed and scanning voltage range on corrosion resistance of PPy film was discussed through method of single factor variable. Electrochemical impedance spectroscopy (EIS) and polarization curves were tested to characterize corrosion resistance of PPy film. The results showed that PPy film on the Mg alloy surface can improve the corrosion resistance. PPy film which prepared circulating 7 cycles between the scanning voltage range of 0V-2V at 7mV/s scanning speed when concentration of Py in electrolyte was 0.15 mol/L displayed the best corrosion resistance. The corrosion current density could reach 1.156×10-8 A/cm2 and corrosion potential was -0.281V.In this paper, PPy/Silane composite film on Mg alloy surface was prepared by using one step cycle voltammetry method. The mixed solution of methanol and water were selected as hydrolysis solvent of ?- (2,3- glycidoxypropyl) trimethoxysilane coupling agent(KH-560).The influences of the hydrolysis time and content of silane coupling agent on the composite membrane performance were investigated. Specimens after electro-polymerized were cured at 60? for 3h.. Electrochemical impedance spectroscopy and polarization curves were measured to characterize corrosion resistance. The mechanism of the polymerization process was analyzed by using IR spectrum.The PPy/Silane composite film which prepared when the volume fraction in hydrolysis solution of KH-560 was 15% and hydrolysis time was 24h could provide better corrosion protection for Mg alloy. Corrosion current density was as low as 5.935×10-10 A/cm2, corrosion potential was -0.576V.Epoxy coating was coated directly on the surface of eligenstate polypyrrole, which denoted as PPy-Epoxy coating. PPy-Silane-Epoxy coating was prepared by coated with KH-560 and epoxy successively on the surface of eligenstate polypyrrole. And PPy/Silane-Epoxy was obtained when epoxy coating was coated on the surface of PPy/Silane.Three kinds of composite coatings were immersed in 3.5% NaCl solution. Electrochemical impedance spectrum and polarization curve in the process of immersion were tested to analysis the mechanism of corrosion protection of PPy-Epoxy, PPy-Silane-Epoxy and PPy/Silane-Epoxy. And the binding force between different composite coating and Mg alloy substrate was compared using Hundred Grid Method.