Plasma electrolytic fluorination on Mg alloys: coating growth and plasma discharge behaviour

• Published in: Surface engineering Vol. 37; no. 11; pp. 1373 - 1387
• Main Authors: Qi, Yuming, Peng, Zhenjun, Liang, Jun, Wang, Peng
• Format: Journal Article
• Language: English
• Published: London, England Taylor & Francis 02.11.2021; SAGE Publications
• Subjects: AZ91 magnesium alloy; coating growth; discharge behaviour; mechanism; non-aqueous electrolyte; optical emission spectroscopy; Plasma electrolytic fluorination; plasma electrolytic oxidation; plasma electrolytic oxidation; discharge behaviour; optical emission spectroscopy; non-aqueous electrolyte; mechanism; coating growth; AZ91 magnesium alloy; Plasma electrolytic fluorination
• ISSN: 0267-0844; 1743-2944
• DOI: 10.1080/02670844.2021.1999078

In this work, plasma electrolytic fluorination (PEF) was performed on AZ91 alloy in a non-aqueous NH 4 F-ethylene glycol (EG) electrolyte. The coating growth and the plasma discharge behaviour were investigated to understand the mechanism of PEF process. Results illustrated that the non-aqueous electrolyte determined the intrinsic characteristics of the PEF process, which resulted in the coating growth characteristics and plasma discharge behaviour distinct from those of a conventional PEO process. MgF 2 compound formed from the combination of the oppositely charged ions Mg 2+ from the substrate and F- form the electrolyte. The deposition of MgF 2 facilitated the growth of the PEF coating with an inward-growth characteristic. The discharge was characterised by a very small size and a weak intensity of the sparks, with an electron temperature (T e ) range of 3400∼3600 K. The three-type discharge model of conventional PEO processes was introduced to understand the mechanism of the PEF process.