Corrosion Behaviour of Preserved PEO Coating on AZ31 Magnesium Alloy

Pastorek, Filip; Štrbák, Milan; Kajánek, Daniel; Jacková, Martina; Pastorková, Jana; Florková, Zuzana

doi:10.26552/com.c.2021.2.b76-b88

Cited by 4 publications

(6 citation statements)

References 41 publications

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“…All measurements were repeated five times. The EIS measurement results are presented in the form of Nyquist and Bode plots diagrams [23][24][25]. The interpretation of impedance data is generally based on the use of EEC (electrical equivalent circuits).…”

Section: Methodsmentioning

confidence: 99%

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Effect of Plasma Electrolytic Oxidation on the Short-Term Corrosion Behaviour of AZ91 Magnesium Alloy in Aggressive Chloride Environment

et al. 2022

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In order to increase the corrosion resistance of magnesium alloy AZ91 in corrosion environments containing chlorides, the alloy surface has been modified by plasma electrolytic oxidation (PEO). The chemical composition of electrolyte in the PEO process consisted of 12 g/L Na3PO4·12 H2O and 1 g/L KOH, and a direct current was applied to the sample. The corrosion resistance of PEO coating and as-cast AZ91 (sample without PEO coating) was assessed using two different electrochemical methods: electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation (PDP) in 0.1 M NaCl at laboratory temperature. In addition to the electrochemical methods, the morphology of the oxidic coating was observed in the cross-sectional and top surface view by using the SEM technique. For better determination of the microstructure and PEO coating, chemical composition EDX analysis was used. The results of the experiments show that the formation of the PEO coating on AZ91 alloy has a more positive effect on the corrosion resistance in 0.1 M NaCl based on electrochemical methods than in the case of the formed coating on AZ31 alloy from the previous study. Based on electrochemical measurements in the selected environment, the formation of PEO coating on AZ91 was accompanied by a significant increase in polarisation resistance after short-term exposure compared to the as-cast surface. The EIS results showed a 73 times higher Rp value for PEO coated AZ91 when compared to the as-cast AZ91. Correspondingly, a 27 times lower icorr value was observed for PEO coated AZ91 than in the case of substrate AZ91 in 0.1 M NaCl. At the same time, the typically porous and inhomogeneous structure of the formed PEO coating on the magnesium alloy AZ91 was demonstrated.

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Section: Methodsmentioning

confidence: 99%

“…Element R s represents electrolyte resistance, and the CPE element is called a constant phase element which is used to replace double-layer capacitance (Cdl). The heterogeneity of the surface, such as roughness, nonhomogeneous composition, etc., significantly affects the value of the constant phase element CPE [24].…”

Section: Methodsmentioning

confidence: 99%

Effect of Plasma Electrolytic Oxidation on the Short-Term Corrosion Behaviour of AZ91 Magnesium Alloy in Aggressive Chloride Environment

et al. 2022

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“…To avoid possible errors in the interpretation, all experiments were repeated three times. Corrosion parameters were determined using Nyquist diagrams, which were quantitatively evaluated using the equivalent circuit technique with EC-Lab V11.10 software [ 5 , 17 , 18 ]. The schematics of circuits used are shown in Figure 2 .…”

Section: Methodsmentioning

confidence: 99%

“…In the more complex circuit with two capacitive loops, it describes the resistance of the pores, which are typical for the further layer of the coating. On the other hand, the element R 2 represents the resistance for charge transfer in the inner layer of the PEO coating [ 4 , 5 , 22 , 23 ].…”

Section: Methodsmentioning

confidence: 99%

“…The main influence of the poor corrosion resistance is caused by the synergistic effect of the standard negative potential of Mg −2.36 V with respect to the standard hydrogen electrode (SHE), the mixture of the natural properties of Mg, the presence of impurities (Fe, Cu, and Ni), and the quasi-protective passive surface film consisting of MgO or Mg(OH) 2 , which provides protection against alkaline pH environments [ 3 , 4 ]. To improve this poor corrosion resistance, many coating techniques were applied, including chemical conversion coatings, anodizing, electroplating, electro-less plating, organic coatings, and fluoride-based coatings [ 5 , 6 ].…”

Section: Introductionmentioning

confidence: 99%

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The Effect of Mechanical Pretreatment on the Electrochemical Characteristics of PEO Coatings Prepared on Magnesium Alloy AZ80

et al. 2023

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The main objective of this article is to provide new information on the effects of mechanical pretreatment of AZ80 magnesium alloy ground with SiC emery papers of different grain sizes on the plasma electrolytic oxidation (PEO) process and corrosion properties of AZ80 in 0.1 M NaCl solution. Then, the roughness of the coated samples was measured by confocal microscopy. The corrosion properties of the ground and coated surfaces were determined by potentiodynamic polarization (PDP) within 1 h of exposure, and electrochemical impedance spectroscopy (EIS) was performed during 168 h of exposure at laboratory temperature. Consequently, the obtained results of the PDP measurements were evaluated by the Tafel analysis and the EIS evaluation was performed by the equivalent circuit analysis through Nyquist diagrams. The morphology and structure of PEO coatings were observed by scanning electron microscopy (SEM) through the secondary imaging technology, and the presence of certain elements in PEO coatings was analyzed by EDS analysis.

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Characterization and corrosion behaviour of a phosphate-based plasma electrolytic oxidation coating on extruded EV31 magnesium alloy

Knap

Štrbák

Hadzima

et al. 2023

International Journal of Materials Research

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This paper is focused on evaluating the surface properties of protective coating prepared by plasma electrolytic oxidation on magnesium alloy EV31. Plasma electrolytic oxidation was performed in DC mode with a constant current density of 0.05 A cm−2 for 14 min. Evolution of voltage was measured and depicted graphically in order to describe the growth of the plasma electrolytic oxidation coating. Morphology and thickness of the plasma electrolytic oxidation coating were examined together with corrosion resistance of the coating by measurements of electrochemical characteristics using electrochemical impedance spectroscopy and potentiodynamic polarization after 1 h in 0.1 M NaCl. Results from potentiodynamic polarization showed decrease in corrosion current density i corr from 10.50 μA cm−2 (substrate) to 1.02 μA cm−2 (plasma electrolytic oxidation coated) and results from electrochemical impedance spectroscopy showed increase in R p by one order of magnitude for plasma electrolytic oxidation coated sample after both 1 h and 168 h exposure times.

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Corrosion Behaviour of Preserved PEO Coating on AZ31 Magnesium Alloy

Cited by 4 publications

References 41 publications

Effect of Plasma Electrolytic Oxidation on the Short-Term Corrosion Behaviour of AZ91 Magnesium Alloy in Aggressive Chloride Environment

Effect of Plasma Electrolytic Oxidation on the Short-Term Corrosion Behaviour of AZ91 Magnesium Alloy in Aggressive Chloride Environment

The Effect of Mechanical Pretreatment on the Electrochemical Characteristics of PEO Coatings Prepared on Magnesium Alloy AZ80

Characterization and corrosion behaviour of a phosphate-based plasma electrolytic oxidation coating on extruded EV31 magnesium alloy

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