Electronic Shell Of Magnesium Alloy Materials, Micro-arc Oxidation Process

In this article, in alkaline silicate electrolyte, using the orthogonal experimental method, through analyzing surface morphology and corrosion resistance of the film which formed on the MB8 magnesium alloy, to determine the best density of the electrolyte. Then in this density electrolyte, using the same method to determine the optimal electrical parameters, thus determined the silicate system, the best micro-arc oxidation process. Through the best process to form micro-arc oxidation film, improved the corrosion resistance of magnesium alloys to some extent, but because of the existence of micro-pores and micro-cracks and other defects on micro-arc oxidation film, provides the channel for the corrosive medium migration. Therefore, using cathode electrophoresis as the post-processing of micro-arc oxidation process, micro-arc oxidation-electro-coating composite coating form on the surface of magnesium alloys In the Potentiodynamic polarization experiments and salt water immersion test, all showed that composite coatings have the best corrosion resistance. Experimental results are as follows:(1) In the electrolyte orthogonal experiments, the order of the various factors impact on film thickness:sodium silicate>potassium fluoride>glycerol>potassium hydroxide. While the order of various factors impact on corrosion resistance as follows:potassium hydroxide>sodium silicate>KF= glycerin. Through analysis the impact of various factors on the morphology and corrosion resistance, the electrolyte optimization results as follows: Sodium 10g/l, potassium fluoride 6g/l potassium hydroxide 6g/l, glycerol 5ml/l.(2) The order of electrical parameters impact on the micro-arc oxidation film thickness: the termination voltage>duty cycle> frequency>current density. While the order of the corrosion resistance as follows:the termination voltage>frequency>duty cycle= current density. Through analysis of the impact of the various factors on the morphology and corrosion resistance, the optimization results of electrical parameter:frequency 400Hz, duty cycle 30%, termination voltage 410V, current density 3A/dm2.(3) On the most optimum process conditions, the micro-arc oxidation film is crystalline structure, composite by MgO, MgSiO4, MgF2, Mg14 (SiO4) 5O4 phases. Composite film compare with the optimized micro-arc oxidation film or MB8 magnesium alloy, corrosion potentials were being moved about 1000mV or 1200mV, respectively, while the corrosion potential decreased by about 5 or 10 orders, respectively. In 5%NaCl solution, the corrosion of micro-arc oxidation film is in the form of pitting+filiform corrosion, micro-arc oxidation-electro-coating composite coating film in the form of filiform corrosion.(4) In micro-arc oxidation process, as the voltage increase, the discharge spark size increase, brightness increase, the color change from bright blue to orange, the number increase first and then decrease, and can be divided into four stages:the traditional anodic oxidation stage, the spark anodizing stage, the micro-arc oxidation stage and the arc oxidation stage.