Unconventional fluoride conversion coating preparation and characterization
Abstract
Purpose
The purpose of this paper is to compare electrochemical corrosion characteristics of conventional and unconventional fluoride conversion coating prepared on magnesium alloy.
Design/methodology/approach
The chemical reaction of AZ61 with 38 wt.% hydrofluoric acid (HF) for 24 h was used as a conventional way of fluoride conversion coating preparation. The unconventionally prepared coating was created in Na[BF4] salt melt at 450°C for 2 h. Morphology and chemical composition of prepared fluoride conversion coatings were studied with scanning electron microscopy and energy-dispersive X-ray spectroscopy. Electrochemical corrosion characteristics of the coatings were analyzed in Hank’s solution using potentiodynamic tests.
Findings
Both the coating preparation ways resulted in the creation of uniform conversion coatings with the same thickness (1.3 ± 0.1 μm). Some defects were observed on the coatings surface; however, the defects did not reach the AZ61 surface. Electrochemical tests performed in Hank’s solution at 37°C showed an improvement of corrosion resistance of AZ61 treated with fluoride conversion coatings when compared to the untreated material. Unconventionally prepared coating reached better electrochemical corrosion characteristics when compared to the conventionally prepared coating.
Originality/value
Electrochemical corrosion characteristics of AZ61 magnesium alloy can be improved with fluoride conversion coatings. Two methods are used in the literature for the coatings preparation. The conventional method is based on dipping of the coated material to the HF, and the unconventional method lies in dipping of the sample to the Na[BF4] salt melt. The main purpose of the present study is to analyze the conventionally and unconventionally prepared coatings in terms of chemical analysis, morphology and material corrosion protection (electrochemical corrosion characteristics), while the data are not provided in the literature, according to the authors’ knowledge. Very similar coatings were prepared using both the methods from the morphological and chemical composition point of view. However, unconventionally prepared coating created in Na[BF4] salt melt reached better electrochemical corrosion characteristics compared to the coating prepared in HF.
Keywords
Acknowledgements
This work was supported by Project Nr. LO1211, Materials Research Centre at FCH BUT-Sustainability and Development (National Program for Sustainability I, Ministry of Education, Youth and Sports of the Czech Republic).
Citation
Drábiková, J., Fintová, S., Tkacz, J., Doležal, P. and Wasserbauer, J. (2017), "Unconventional fluoride conversion coating preparation and characterization", Anti-Corrosion Methods and Materials, Vol. 64 No. 6, pp. 613-619. https://doi.org/10.1108/ACMM-02-2017-1757
Publisher
:Emerald Publishing Limited
Copyright © 2017, Emerald Publishing Limited