AZ31B magnesium alloy micro-arc oxidation ceramic coating after the preparation and sealing technology research

Title: AZ31B magnesium alloy micro-arc oxidation ceramic coating after the preparation and sealing technology research Author: Qi Sufang Degree-granting unit: Harbin Institute of Technology Key words: magnesium alloy;; micro-arc oxidation;; sealing;; corrosion resistance Summary:

Magnesium has many excellent properties, but due to poor corrosion resistance limits its wider application. The issue for the poor corrosion resistance of magnesium alloy problem in Na2SiO3 electrolyte system, the use of micro-arc oxidation Neodymium Magnets method and sealing technology in AZ31B magnesium alloy sheet surface corrosion resistance of the film prepared in situ to study the micro-arc oxidation process parameters, Ce doping and sealing process on the film structure and properties of the law, and the film in 3.5% NaCl solution in the preliminary analysis of the corrosion mechanism.

X-ray diffraction (XRD), scanning electron microscopy (SEM), electron spectroscopy (EDS), test methods, analysis of the film phase and elemental composition of the observed ceramic coating surface and cross section morphology; the use of eddy current thickness test film thickness; use of scarification, heat shock experiments investigated the binding force of the film, using CHI660 electrochemical tester, salt spray corrosion resistance of ceramic membrane can be.

The results show that the micro-arc oxidation ceramic coating mainly composed of MgO and Mg_2SiO_4 two-phase, porous structure. Ceramic film thickness, roughness with reaction time, increased with increasing current density; as the frequency increases, the ceramic coating thickness decreases, the roughness decreases; As the duty cycle increases, the ceramic film thickness and roughness showed the first increase and then decreased. To uniform corrosion and electrochemical corrosion test methods for evaluating the optimization of process parameters, the result is a frequency of 300Hz, 45% duty cycle, current density 2A/dm ~ 2, the reaction time was 5min, optimization of process parameters prepared ceramic membrane compared with the magnesium matrix, corrosion current density three orders of magnitude lower. The use of cerium conversion coating, the electrolyte by adding cerium, cerium and other methods to expand penetration in the introduction of Ce in the ceramic membrane, the results show that the micro-arc oxidation before the cerium conversion coating, not only can reduce the arc voltage, and can improve the corrosion resistance .

By boiling water sealing, impregnation - sealing dip coating method, air sealing methods such as spray coating on the ceramic sealing, boiling water sealing structure of the ceramic coating and corrosion resistance is not obvious, dip - dip coating seal holes in the ceramic coating can be formed on the surface coating layer 2 ~ 5μm, in part or all of the ceramic http://www.everbeenmagnet.com/en/products/110-sintered-neodymium-magnets coating to seal the surface of the hole, making the corrosion resistance of the film has significantly improved. Sealing air spray paint ceramic coating can be formed on the surface coating layer of about 15μm, could seal the entire surface of the hole blocking layer can greatly improve the corrosion resistance of the film, the film can maintain 144h salt spray test in good condition. Degree Year: 2010