졸-겔 코팅과 인산망간피막 처리 된 마그네슘 합금의 부식 방식 연구

Abstract

Magnesium alloys possess many excellent properties, such as low density, high specific strength, shielding effectiveness, good casting ability, machinability, and damping capacity, etc. Thus, it is used to various fields such as automotive, aircraft, electronic field and sports and others which need to design, mold, painting, fabricating skills. Magnesium standard electrode potential has –2.363V vs. NHE at 25℃ (Normal Hydrogen Electrode). High electrochemical activity caused to fast passivated with oxygen in air. It has greatly limited. So, it is necessary for magnesium alloys to have surface treatments and various coatings to prevent corrosion. In this paper, chemical conversion was coated by phosphate and permanganate solution. Sol-gel coating was prepared using (3-glycidyloxy propyl)trimethoxysilane, methyltrimethoxysilane and aluminum tri-sec-butoxide as precursors, acetyl acetone as chelating agent. Corrosion protection effects of conversion coating, conversion coating/sol-gel coating double layer, sol-gel coating on AZ31 was investigated in 0.35 wt% NaCl solution. Electrochemical properties of coating layers were measured by electrochemical impedance spectroscopy and potentiodynamic polarization test. Surface properties were analyzed by scanning electron microscopy, X-ray diffraction, X-ray fluorescence and X-ray photoelectron spectroscopy. Electrochemical properties showed that the conversion coating/sol-gel coating double layer was significantly improved the corrosion resistance and optimal performance in the corrosion rate. According to the surface properties test, conversion coating/sol-gel coating double layer also have optimized properties. While immersed in NaCl solution, double layer have no fracture, defects and better retain the layer rather than conversion coating and sol-gel coating single layer.