Microstructure, Hardness, and Corrosion Behavior of Oxidized AA6061 Using Potentiostatic Plasma Electrolytic Oxidation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Reviewer comments

Manuscript ID coatings-3784435

 

The paper analyzes the methods of forming coatings on aluminum and its alloys and singles out plasma electrolytic oxidation (PEO). A review of literature sources is conducted, which describe both PEO processes and the properties of oxide coatings, in particular corrosion. The aluminum alloy AA6061, the composition of the electrolyte, electrical and temperature regimes of PEO coating formation were selected for the research. The microstructure and corrosion behavior of the aluminum alloy AA6061 were studied at different voltages in an alternating current source in the potentiostatic mode. PEO treatment was carried out at a constant frequency, duty cycle and treatment time in a silicate-based electrolyte: 5 g/l Na₂SiO₃ and 5 g/l KOH. The applied potentials were determined based on the breakdown voltage of AA6061 taking into account the properties of the electrolyte. The surface morphology, elemental and phase composition of the PEO-coated samples on AA6061 were investigated using SEM, EDX, and XRD. The corrosion behavior of the PEO-coated samples on AA6061 was studied using potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5 wt.% NaCl solution. The Vickers hardness of untreated and PEO-coated AA6061 samples was measured using a microhardness tester.

 

The article is interesting and can be accepted after minor revisions (corrections to minor methodological errors and text editing).

 

Comment 1. In the introduction, information should be added about Optimization of Plasma Electrolytic Oxidation Technological Parameters of the process of forming coatings on aluminum alloys, which would enrich this article.

Comment 2. In the second section, the item (2.2 Substrate preparation) does not indicate the parameters of the surface roughness of the aluminum alloy before PEO.

Comment 3. Line 130 … The substrates were then etched in nitric acid (500 ml of 67% HNO₃ in 1L of distilled water) for 3 minutes, rinsed with deionized water and air dried. Explain the need for such acid etching treatment, and what were the surface roughness parameters of the aluminum substrate?

Comment 4. Line 136. The PEO electrolyte consisting of 5 g/L Na₂SiO₃ and 5 g/L KOH was used for this study. It is known that the properties of PEO coatings, in particular corrosion protection, depend on the component composition of the electrolyte. It is necessary to explain what was the reason for choosing only one fixed composition of the electrolyte?

Comment 5. Section 2.4 PEO process. It is known that the properties of PEO coatings, in particular corrosion protection, also depend on the voltage and current density. It is necessary to explain what was the reason for choosing only two fixed voltage values (350 V and 400 V) for the research?

Comment 6. In Figures 1, 4, improve the labels on the scale bars.

Comment 7. In Figure 5, improve/increase the labels on the scale bars, as well as the numbers and letters on the two spectra.

Comment 8. In the paper, the “hyphen” symbol should be replaced with the mathematical symbol “minus” both in the text and in the graphs.

Comment 9. And finally, it is necessary to add a discussion to enrich this article.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Presented paper is well-written and contains some interesting results. Moreover, the authors approached the setting up of experiments and description of results with great attention. There are only few comments to the paper (please see below).

Lines 43-45. I would be great, if authors add some recent papers connected with PEO treatment of different alloys (for example, https://doi.org/10.1016/j.jma.2024.05.006 or others).

3. Result. Please change name of the section to Results and Discussion, since separate Discussion section is absent and all discussions of obtained results are provided in section 3.

Fig. 1 and 4. Please make the scale bars dimension is more distinguishable.

Fig. 2. Is this Fig. from Sobolev et al work? If so, please provide permission.

Fig. 5. Please provide scale bar. EDS data from bottom part is poor visible. The reviewer recommends to provide in a table form.

Fig. 6. Please delete a.u. since there is no numerical values and two samples are presented in one fig.

Author Response

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Author Response File: Author Response.pdf