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Electronic shell material magnesium alloy micro-arc oxidation and subsequent treatment process research

Author: HeYi
Tutor: WuLianBo
School: Changchun University of
Course: Materials Science
Keywords: Magnesium alloy Micro-arc oxidation Electrical parameters Corrosion resistance Electrophoretic coating
CLC: TG174
Type: Master's thesis
Year: 2010
Downloads: 96
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Abstract


In this paper, the alkali silicate system, orthogonal experimental method, the analysis MB8 Mg alloy layer formed on the surface morphology and corrosion resistance, to determine the optimal concentration of the electrolyte. Then at this concentration of the electrolyte, using the same method to determine the optimal electrical parameters, which determine the silicate system the best micro-arc oxidation process. By optimum formation of micro-arc oxidation film, to some extent improved the corrosion resistance of magnesium alloys, but because there micro-arc oxidation film microscopic pores and cracks and other defects, which is corrosive media provides a migration path. Therefore, the use of micro-arc oxidation cathodic electrodeposition as a post-processing step of forming a magnesium alloy sample surface micro-arc oxidation - electrophoretic coating composite coating. Potentiodynamic polarization experiments and brine experiments indicate that the composite film has the best corrosion resistance. Experimental results are as follows: (a) electrolyte orthogonal experiment, the influence of film thickness on the order of: sodium silicate gt; potassium fluoride gt; glycerol gt; potassium hydroxide. While the corrosion resistance of order: potassium hydroxide gt; sodium silicate gt; potassium fluoride = glycerol. The morphology by various factors, the analysis of the corrosion resistance of the electrolyte optimal results: sodium silicate 10g / l, potassium fluoride, 6g / l, potassium hydroxide 6g / l, glycerol 5ml / l. (2) electrical parameters of micro-arc oxidation film thickness of order: termination voltage gt; duty gt; frequency gt; current density. While the corrosion resistance of order: termination voltage gt; frequency gt; Duty Cycle = current density. Through the various factors on the morphology, the analysis of the impact of corrosion resistance, electrical parameters optimization results as: frequency 400Hz, 30% duty cycle, the termination voltage 410V, current density 3A/dm2. (3) the optimal process conditions, the formation of micro-arc oxidation film of crystalline structure, consisting of MgO, MgSiO4, MgF2, Mg14 (SiO4) 5O4 phase composition. Composite film with optimized micro-arc oxidation film and MB8 magnesium alloy, corrosion potentials shifted positively about 1000mV and 1200mV, while the corrosion potential is decreased by approximately 5 and 10 orders of magnitude. In 5% NaCl solution, micro-arc oxidation film pitting corrosion in the form of filiform corrosion. Micro-arc oxidation - electrophoretic coating composite film of corrosion in the form of filiform corrosion. (4) micro-arc oxidation process, as the voltage increases, the discharge spark size increases, increased brightness, color changes from blue to white to orange, the number of first increases and then decreases. And can be divided into four stages: the traditional anodic oxidation stage, sparks anodic oxidation stage, micro-arc oxidation stage and arc oxidation stage.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection
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