Effect of Electrolyte in Microarc Oxidation on Providing Corrosion Resistance to Inhomogeneous Microstructure in ZM21 Magnesium Alloy

摘要

Microarc oxidation (MAO), an electrochemical process that employs aqueous electrolytes, is adopted to impart corrosion resistance to magnesium alloys. To study the influence of the inhomogeneity in the microstructure on the characteristics of the coating and therefore on the properties, the weld of a ZM21 alloy was considered. The surfaces of the weld metal and the base metal were treated using MAO with silicate and phosphate-based electrolytes. Corrosion behavior of the coated and uncoated base metal and weld metal in 0.1M NaCl was compared using potentiodynamic polarization tests. The results showed that the inhomogeneity in the microstructure of the substrate altered the nature of the coatings and their corrosion resistance was not the same for the electrolytes used in MAO. While for the silicate-based electrolyte, the coated weld metal showed better corrosion resistance than the base metal; a reversal in the corrosion property was noticed with phosphate-based electrolyte.