Formation of a corrosion-resistant coating on zinc by a duplex plasma electrolytic oxidation and conversion surface treatment

A two-step, environmental-friendly process is proposed to improve the corrosion resistance of zinc. The first step involves plasma electrolytic oxidation (PEO), to produce a uniform 6 μm thick ZnO layer in a short processing time of 30 s. This is followed by a conversion treatment by immersion in 1 ...

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Bibliographic Details
Published in:Surface & coatings technology 2020-08, Vol.395, p.125918, Article 125918
Main Authors: Joseph, Jithin, Gallo, Santiago Corujeira, Catubig, Rainier, Wang, Ke, Somers, Anthony, Howlett, Patrick, Fabijanic, Daniel
Format: Article
Language:English
Subjects:
Conversion treatment
Corrosion resistance
Electrochemical impedance spectroscopy
Electrode polarization
Morphology
Open circuit voltage
Oxidation
Oxidation resistance
Patina
Phase composition
Plasma electrolytic oxidation
Protective coatings
Scratch resistance
Scratch testing
Sodium bicarbonate
Submerging
Surface coating
Surface layers
Surface treatment
Zinc
Zinc coatings
Zinc oxide
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Summary:A two-step, environmental-friendly process is proposed to improve the corrosion resistance of zinc. The first step involves plasma electrolytic oxidation (PEO), to produce a uniform 6 μm thick ZnO layer in a short processing time of 30 s. This is followed by a conversion treatment by immersion in 1 M sodium bicarbonate solution for 1 h at open circuit potential. The morphology, thickness and phase composition of the surface layers were analysed using scanning electron microscopy and X-ray diffraction. The electrochemical tests (potentiodynamic polarisation and electrochemical impedance spectroscopy) showed enhanced corrosion resistance of the PEO coating after the conversion treatment. The improved corrosion resistance was attributed to the sealing of defects during the conversion treatment and the partial conversion of the ZnO layer into a protective patina. The PEO and duplex treatments also imparted a mechanically durable coating with higher scratch resistance compared to the conversion treatment. [Display omitted] •The PEO treatment can rapidly form a 6 μm thick ZnO layer on zinc substrates.•Subsequent immersion treatment in sodium bicarbonate solution seals micro-defects formed during PEO.•The mechanically durable coating formed upon duplex treatment improves the corrosion resistance.
ISSN:0257-8972
1879-3347
DOI:10.1016/j.surfcoat.2020.125918