Influence of electrolyte on corrosion properties of plasma electrolytic conversion coated magnesium alloys

Abstract

The synthesis of oxides in a low-temperature electrolytic plasma allows to cover surfaces of magnesium and its alloys with multifunctional protective oxide-ceramic coatings. The corrosion properties of these layers are strongly dependent on their porosity. In order to minimize the porosity and to optimize the corrosion properties of the layers, the electrolyte concentration and composition (addition of CrO 3 as corrosion inhibitor) were varied, and the influences on layer structure, composition, and properties with a main focus on corrosion behaviour were studied. The corrosion properties of various layers thus generated were studied in 5% NaCl solution by measuring electrochemical polarization curves and by electrochemical impedance spectroscopy (EIS) at pH 3 and 6. Using XRD, LM, SEM and EDX to evaluate the composition and microstructure of the modified surfaces, the corrosion results were related to the microstructure and composition of the specific layer. The better results were obtained for layers produced at higher electrolyte concentration, whereas the addition of CrO 3 had no significant beneficial effect.

Effect of current density and behaviour of second phases in anodizing of a Mg-Zn-RE alloy in a fluoride/glycerol/water electrolyte

“…However, surface treatment is often required in order to provide the requisite corrosion protection. Electrolytic processes, such as anodizing and plasma electrolytic oxidation, are commonly employed, and a variety of processes is available that produce relatively thick, porous coatings under dielectric breakdown [1][2][3][4][5], which are usually used as part of a coating system. The coatings are also of interest for biodegradable magnesium implants, enabling control of the corrosion rate and enhancing the biocompatibility [6,7].…”

Stress corrosion cracking behaviour of a surface-modified magnesium alloy

“…A good number of surface modification procedures have been developed and contemplated with a reasonable degree of success for different applications [7][8][9]. The plasma electrolytic oxidation (PEO) treatment has been found to be quite effective in improving the tribological and corrosion properties of magnesium alloys [10][11][12]. Even though many researchers have assessed the general corrosion behaviour of PEO coated magnesium alloys, there seems to be no published information on the stress corrosion cracking behaviour of magnesium alloys with PEO coating available.…”

The protective properties of coatings on a magnesium alloy formed by plasma electrolytic oxidation in silicate electrolytes

“…Despite the large number of works in this field [7][8][9][10][11][12], the issue of the influence of electrolyte composition and modes of PEO treatment on the protective properties of coatings on magnesium alloys and justification of optimal conditions of their formation are still topical.…”