The role of cathodic current in PEO of aluminum: Influence of cationic electrolyte composition on the transient current-voltage curves and the discharges optical emission spectra

Rogov, Aleksey B.; Shayapov, V. R.

doi:10.1016/j.apsusc.2016.10.115

Cited by 46 publications

(38 citation statements)

References 27 publications

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“…The absolute value of the negative voltage decreased and the electric conductivity of the electrolyte sharply increased in Stage IV. 38 This phenomenon may be attributed to the increase in the concentration of cations in the alkaline electrolyte, which originated from the dissolution of the substrate with the increase in the PEO time. Therefore, it required relatively low energy for the initiation of microdischarges.…”

Section: Resultsmentioning

confidence: 99%

Effect of the Cu Content on the Microstructure and Corrosion Behavior of PEO Coatings on Al–xCu Alloys

Zhu

Zhang

et al. 2018

J. Electrochem. Soc.

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In this study, scanning electron microscopy and electrochemical techniques were used to investigate the effect of the Cu content on the microstructure and corrosion resistance of plasma electrolytic oxidation (PEO) coatings on Al-xCu alloys. The results showed that Cu in the substrate alloy was used to promote the intensity and the transformation process of the microdischarges, which led to the undulating-ribbon feature of cross-sectional morphologies. The formation of pores and cracks in the coatings was facilitated by the oxygen release due to the oxidation of O 2− and the dissolution of copper oxide. Meanwhile, the average porosity of PEO coatings distinctly increased with the increase in the Cu content, which is the key factor causing the decreased corrosion resistance of PEO coatings. Due to their high strength to weight ratio, Cu-containing aluminum alloys are one of the most promising materials for use in aerospace and automobile applications. However, their application is limited by low corrosion resistance. Therefore, plasma electrolytic oxidation (PEO) is considered to be a well-known process for the in situ production of oxide coatings on Al and its alloys, which can offer better corrosion protection as compared to the other surface modification processes for substrate alloys. [1][2][3][4] In general, many processing factors, such as the composition of electrolyte, 5-7 additives, 8-10 applied power modes, 11-13 electrical parameters, 14,15 temperature, 16 and oxidation time, 17 are used to control the PEO process. These parameters not only affect the PEO process but also the performance of the prepared coatings. The characteristics of the formed PEO coatings could also be affected by the alloying elements in substrate alloys. However, this has not been studied in much detail. To the best of our knowledge, the literature contains several papers that describe the effect of multiple elements (such as Si, Mg, Cu, Li, and Fe) on the properties of the formed PEO coatings for commercial aluminum alloys.18-20 While, only a few studies focused on the effect of single alloying element in substrate. Among others, Ali et al. studied the PEO treatment of simple binary Al-Si alloys and reported that the thickness of PEO coatings significantly decreased, whereas their porosity increased with the increase in the Si content. The decomposition of volatile silicon oxides, such as SiO in the formed coatings during the PEO process, contributed to the high porosity. Furthermore, Si exhibits low electrical conductivity, which adversely affects the formation of microdischarges and the oxidation kinetics of the alloy. 21 Meanwhile, Oh et al. studied the effect of Mg on the properties of PEO coatings on Al-Mg alloys and demonstrated that when the amount of Mg was higher than 3 wt% the formation of α-Al 2 O 3 was inhibited.22 It is also reported that Zn is the primary alloying element for the 7××× series Al alloys, and the peculiar function of Zn during the formation of PEO coatings on binary Al-Zn alloys has also been investig...

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Section: Resultsmentioning

confidence: 99%

Effect of the Cu Content on the Microstructure and Corrosion Behavior of PEO Coatings on Al–xCu Alloys

Zhu

Zhang

et al. 2018

J. Electrochem. Soc.

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“…Even though cations do not contribute directly to the oxide growth, they indirectly affect the interface resistance and capacitance. Rogov and Shayapov [51] showed that the rectification (valve) effects were pronounced for Na + and K + ions, less for Li + and Et 4 N + , and worst for Ca 2+ . A large hysteresis was observed on CVCs of Na + and K + , but not Et 4 N + and Ca 2+ during the micro-arc stage.…”

Section: The Cathodic Current Sets the Tonementioning

confidence: 99%

Review of the Soft Sparking Issues in Plasma Electrolytic Oxidation

Tsai

Chou

2018

Metals

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Abstract:A dense inner layer is highly valued among the surface coatings created through plasma electrolytic oxidation (PEO) treatment, because the PEO coating has been troubled by inherent porosity since its conception. To produce the favored structure, a proven technique is to prompt a soft sparking transition, which involves a sudden decrease in light and acoustic emissions, and a drop in anodic voltage under controlled current mode. Typically these phenomena occur in an electrolyte of sodium silicate and potassium hydroxide, when an Al-based sample is oxidized with an AC or DC (alternating or direct current) pulse current preset with the cathodic current exceeding the anodic counterpart. The dense inner layer feature is pronounced if a sufficient amount of oxide has been amassed on the surface before the transition begins. Tremendous efforts have been devoted to understand soft sparking at the metal-oxide-electrolyte interface. Studies on aluminum alloys reveal that the dense inner layer requires plasma softening to avoid discharge damages while maintaining a sufficient growth rate, a porous top layer to retain heat for sintering the amassed oxide, and proper timing to initiate the transition and end the surface processing after transition. Despite our understanding, efforts to replicate this structural feature in Mg-and Ti-based alloys have not been very successful. The soft sparking phenomena can be reproduced, but the acquired structures are inferior to those on aluminum alloys. An analogous quality of the dense inner layer is only achieved on Mg-and Ti-based alloys with aluminate anion in the electrolytic solution and a suitable cathodic current. These facts point out that the current soft sparking knowledge on Mg-and Ti-based alloys is insufficient. The superior inner layer on the two alloys still relies on rectification and densification of aluminum oxide.

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“…Under soft sparking conditions (R > 1 for Al), there is a "critical point" in the process, after which coating growth is accompanied by a decrease in anodic voltage. The latter is probably counterintuitive, since breakdown voltage is expected to increase with coating thickness; however, phenomena underlying the role of cathodic (negative) current are quite complex, and few attempts of its analysis were performed [56][57][58].…”

Section: Load Analysismentioning

confidence: 99%

Smart Arbitrary Waveform Generator with Digital Feedback Control for High-Voltage Electrochemistry

Rogov¹

2019

Instruments

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This paper describes a design approach to a control system of power supply for high-voltage electrochemical processes such as plasma electrolytic oxidation (PEO) or high-voltage anodising (HVA), which require alternating polarisation pulses up to 750 V and a typical current density of 50–500 mA/cm2. Complex characteristics of the electrochemical system response on applied polarisations (positive or negative) cause necessity of precise control of polarising pulse shapes for better process operation and its understanding. A device performs cycle-by-cycle pulse-width modulation (PWM) control, including feedback based on digital analysis of the instantaneous current and/or voltage output, and the desired pulse waveform stored in memory for each output polarity. The output stage has four states corresponding to positive or negative pulses, as well as open- or short-circuit conditions, with respect to an electrochemical cell. A fully programmable controller allows one to generate arbitrary waveforms, as well as their sequences, by means of “regime designer” software. Moreover, a smart feedback system can provide adaptation of the next pulse parameter from analysis of the process prehistory. For instance, this approach allows one to separate main electrochemical process (coating formation) and diagnosis of the phenomenon through introduction of high-voltage triangular voltage sweep pulse within a pause of the main process, which is normally carried out under a current control.

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The role of cathodic current in PEO of aluminum: Influence of cationic electrolyte composition on the transient current-voltage curves and the discharges optical emission spectra

Cited by 46 publications

References 27 publications

Effect of the Cu Content on the Microstructure and Corrosion Behavior of PEO Coatings on Al–xCu Alloys

Effect of the Cu Content on the Microstructure and Corrosion Behavior of PEO Coatings on Al–xCu Alloys

Review of the Soft Sparking Issues in Plasma Electrolytic Oxidation

Smart Arbitrary Waveform Generator with Digital Feedback Control for High-Voltage Electrochemistry

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