Abstract
The effect of the addition of alcohol to a Na3PO4-based electrolyte on plasma electrolytic oxidation (PEO) of AZ31B magnesium alloy was investigated. Anodization with spark discharge was conducted in Na3PO4-based electrolyte containing various alcohols (e.g., ethanol, ethylene glycol, and glycerol) at a constant current density of 200 A m−2 and a constant temperature of 25 °C. Voltage–time curves during the PEO process, the film structure, surface roughness, crystallographic structure, composition, corrosion resistance, and withstand voltage were investigated using various analytical equipment and electrochemical measurements. When the electrolyte containing alcohol was used, the initial bending voltage was higher than that observed using the basic electrolyte without alcohol addition, as was the oscillation voltage during the PEO process. For a given amount of electricity supplied, the addition of alcohol into the basic electrolyte tended to increase the thickness and corrosion resistance of PEO films formed while effectively reducing surface roughness. In particular, the addition of a polyhydric alcohol (i.e., ethylene glycol and glycerol) could act not only as a leveler for the formation of compact film but also as an enhancer for film qualities, such as corrosion resistance and withstand voltage. The patterns observed for Na3PO4-based electrolyte containing alcohol also hold for Na2SiO3-based electrolyte containing alcohol.
Highlights
Magnesium and its alloys have attracted attention as lightweight materials with various advantages, such as low density, high strength-to-weight ratio, and substantial recyclability
We investigated the microstructures and corrosion resistance of the anodic oxide lms formed on AZ31B magnesium alloy by direct current (DC) anodization under continuous sparking in alkaline phosphate electrolyte.[27,28,29]
The effect of electrolysis conditions on the electrochemical formation behavior, microstructure, thickness, composition, and corrosion resistance of anodic lms formed on AZ31B magnesium alloy was investigated with a focus on the addition of alcohols to the electrolyte
Summary
Magnesium and its alloys have attracted attention as lightweight materials with various advantages, such as low density, high strength-to-weight ratio, and substantial recyclability. The effect of electrolysis conditions on the electrochemical formation behavior, microstructure, thickness, composition, and corrosion resistance of anodic lms formed on AZ31B magnesium alloy was investigated with a focus on the addition of alcohols to the electrolyte. This focus has been relatively little studied compared with the numerous PEO studies using uoride or particles as additives,[20,21,22,23,24,25,26] especially with respect to the properties of the formed lms. Corrosion resistance and passivity were evaluated by simple salt immersion tests and voltage sweeps instead of typical electrochemical tests (e.g., potentiodynamic polarization and electrochemical impedance spectroscopy measurement using a three-electrode system)
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