Conversion coatings of stannates or permanganates were carried out to improve the corrosion resistance of AS21X magnesium alloy. The corrosion behaviour of the treated alloy was studied in 0.1 N solutions of sodium sulphate or chloride mainly by electrochemical methods (e.g. polarization curves and impedance measurements). The best operative conditions for conversion coating formation were determined and successively the coated alloys were subjected to 24 h immersion in the aggressive solutions. Short treatments produced coatings that inhibited mainly the cathodic reaction in the case of permanganate or the anodic reaction in the case of stannate. Optimum coating conditions formed layers which retarded both the anodic and the cathodic corrosion reactions. Protective conversion coatings, particularly towards sulphates, were obtained with the stannate treatment, which produced a uniform layer of MgSnO3. The permanganate treatment caused good results at short testing times because its coating was full of micro-flaws.

Electrochemical study of stannate and permanganate conversion coatings on AS21X Mg alloy

ZUCCHI, Fabrizio;GRASSI, Vincenzo;FRIGNANI, Alessandro;TRABANELLI, Giordano
2005

Abstract

Conversion coatings of stannates or permanganates were carried out to improve the corrosion resistance of AS21X magnesium alloy. The corrosion behaviour of the treated alloy was studied in 0.1 N solutions of sodium sulphate or chloride mainly by electrochemical methods (e.g. polarization curves and impedance measurements). The best operative conditions for conversion coating formation were determined and successively the coated alloys were subjected to 24 h immersion in the aggressive solutions. Short treatments produced coatings that inhibited mainly the cathodic reaction in the case of permanganate or the anodic reaction in the case of stannate. Optimum coating conditions formed layers which retarded both the anodic and the cathodic corrosion reactions. Protective conversion coatings, particularly towards sulphates, were obtained with the stannate treatment, which produced a uniform layer of MgSnO3. The permanganate treatment caused good results at short testing times because its coating was full of micro-flaws.
AS21X; magnesium alloy; electrochemical tests; stannate; permanganate bath
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/1193600
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