Research Of Non-immersiving Roller Brush Micro Arc Oxidation On Magnesium Alloy

With low density, high specific strength and specific rigidity, great heat dissipationperformance and recyclability, magnesium alloys have a profound developing value. However,he low electrode potential and poor corrosion resistance substantially limits furtherapplications of magnesium alloy. Micro arc oxidation(MAO), as a new surface treatmenttechnique developed from the common anodic oxidation, has been generally recognized as themost promising surface treatment to produce a ceramic, adherent coating on Al, Mg, Ti andtheir alloys. By use of micro-arc oxidation on magnesium alloy， the corrosion resistance ofmagnesium alloys can be greatly improved, which could realize the best performance ofmagnesium alloys and also promote the application of magnesium alloys as structuralmaterials.MAO is an anodizing process during which micro-discharges generate dielectricbreakdown of the anodic oxide film under high electric field. As a result, it is difficult toprocess large-scale work-piece in the suggested electrical regime. In this paper, a noval rollerbrush micro arc oxidation (RBMAO) has been proposed to process work-piece with large area.The design of RBMAO is fouces on the structural of the roller brush cathode, the achievementof smooth movement of cathode and the selection of solution exchange circulatory system.Different from the traditional immersing mirco arc oxidation, the roller brush cathodecontains a small-round size stainless steel cylinder with several leak holes， whichconcentrates the electric field on the local area of the large area work-piece. Water absorptionpyroxylin, wrap on the stainless steel cylinder cathode serves as the medium of runningsolution. The running solution form a conductive loop between the water absorptionpyroxylin，work-piece and the cylinder cathode. In addition, the distance of cathode andanode is conducted by the thickness of glue cotton.Solution composition and additives play a key role in micro-arc oxidation process.100g/L NaOH as basic solution, compounded with all kind of ingredients, employing Voltagestep micro arc oxidation method to filter the low-voltage range of AZ91D magnesium alloyand select the preferable solution system and its density. With the established low-voltagerange and the preferable solution, the feasibility of the RBMAO has been verified. In addition,the influences of the anode-cathode space of RBMAO on the surface morphology of AZ91Dmagnesium alloy has been investigated.