Microstructure and Corrosion Behavior of PEO-Coated AA7075 Under Pulsed Unipolar Potential Control Mode
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis manuscript has great innovative significance in investigating microstructure and corrosion behavior of PEO coated AA7075. The work can arouse wide interests of researchers in design and preparation of new protective coatings on aluminum alloys. The manuscript is interesting. In my frank opinion, the manuscript should be deserved for its final publication in such high-level Journal. However, the main comments to be solved are as follows:
1. Why just choose a low and high voltage of 425 V and 450 V? A series of voltage values should be set to explore the detailed variation law of coating morphology and pores.
2. If possible, the pore density in Fig. 3 should be provided error bars.
3. The figures are hard to distinguish for connecting each other.
4. Potentiodynamic polarization curve of bare AA7075 is hard to be understood.
5. If these coatings are immersed in the solution for a long period, how will the surface change?
6. How is the repeatability of electrochemical test in Figs 7 and 8? Please provide the error bars of the values in Tables 4 and 5.
7. The reference is a little outdated, please update it. As seen in introduction about “Aluminum (Al) and its alloys are the most widely used in different applications in marine, aerospace, automotive, metal packaging and transportation industries due to its unique properties owing to its low density (2.7 g/cm3), high specific strength, and thermal and electrical conductivities [1-3].”, such as:
Yang, H.; Dong, Y.; Li, X.; He, W.; Liu, Y.; Mu, X.; Zhao, Y.; Wang, X.; Yang, F.; Fu, W.; Gao, Y.; Qin, W. Enhancing tribological performance of AA3003 aluminum alloy via adjusting surface wettability: Synergistic effects of chemical etching and modification. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2024, 696, 134330. https://doi.org/10.1016/j.colsurfa.2024.134330.
This article points out the application range of aluminum alloys, hence the above reference should be quoted and added for great correlation.
Comments on the Quality of English LanguageEnglish language should be further improved.
Author Response
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Reviewer 2 Report
Comments and Suggestions for AuthorsLacks Detailed Methodological Justification:
- The article does not provide a thorough justification for the chosen experimental parameters, particularly why specific voltages, frequencies, and duty cycles were selected for the PEO process. This omission weakens the rationale behind the experimental design.
- Reference: "Materials and Methods" (p. 3, heading 2.1), "Materials and PEO Process" (p. 3, heading 2.1)
· Insufficient Data on Initial Surface Quality:
- The study inadequately details the initial surface quality and preparation of the AA7075 substrates before the PEO process. This lack of information makes it difficult to assess the consistency and reliability of the experimental results.
- Reference: "Materials and Methods" (p. 3, heading 2.1), "Materials and PEO Process" (p. 3, heading 2.1)
· Overlooks Long-Term Durability Insights:
- The article fails to address the long-term durability and performance of the PEO-coated AA7075 beyond the initial corrosion tests. This limitation prevents a comprehensive understanding of the coating's behavior over extended periods in real-world conditions.
- Reference: "Conclusions" (p. 12, heading 5)
· Neglects Environmental Impact Assessment:
- The research does not evaluate the environmental impact of using PEO-coated AA7075, such as potential benefits in reducing corrosion-related failures and maintenance. Including such an assessment would strengthen the argument for its sustainability.
- Reference: "Introduction" (p. 1, heading 1)
· Inadequate Comparative Analysis:
- The article does not provide a robust comparative analysis between PEO-coated AA7075 and other surface treatment methods in various environmental conditions. More detailed comparisons would help in better understanding the advantages and disadvantages of the PEO coating.
- Reference: "Results and Discussions" (p. 4, heading 3), "Corrosion behavior of PEO-coated AA7075" (p.8, heading 3.3).
Moderate
Author Response
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Reviewer 3 Report
Comments and Suggestions for Authors
The text is written in good scientific language. However, it is not without errors and short comings. Below are the aspects to be addressed and improved.
Page 10
Figure 8 - please use one form of describing of points b and c. We propose: log (f) [Hz] below the horizontal line in both pictures.
Page 11
Table 5 – please describe the symbol: F.s(a - 1)/ - it is unclear
Important
Please use one version of the name image j (line: 195) or ImageJ (line: 145).
The results obtained are original and very important for cognitive and applications aim.
I recommend the paper for publication after the corrections will be made.
Page 1, line 43
Is: …coating technology technique…
Should be: …coating technology… (technique means the same in this context)
Page 1, line 50
Is: Electrical parameters play an important role in how voltage breakdown, local melting 50 and oxidation of substrates will be achieved during the process.
Should be: Electrical parameters play an important role in phenomena like voltage breakdown, local melting and oxidation of substrates which will be achieved during the process.
Author Response
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Reviewer 4 Report
Comments and Suggestions for Authors1) Please explain in more detail the novelty of this work
2) Why did you select 425 and 450 V for the PEO formation?
3) Higher magnification images of the cross section of PEO coatings are required. This will help to illustrate the coatings adhesion to the substrate and the coatings morphology. It will also help expanding the microstructural analysis.
4) SEM images of corroded surface and/or the cross sections after polarization are needed to expand the discussion on the corrosion performance.
5) What is the Epit of the coatings and the alloy?
6) The position of section 3.4 seems odd. It would be more suitable for the 3.1 section and possibly the experimental section.
7) What is the corrosion performance of the coatings as compared to other PEO coatings deposited with similar processes and parameters?
8) Increasing the coating voltage further may enhance corrosion resistance even more?
Author Response
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Reviewer 5 Report
Comments and Suggestions for AuthorsThe manuscript under review explores the microstructure and corrosion behavior of Plasma Electrolytic Oxidation (PEO) coatings on AA7075 aluminum alloy using a pulsed unipolar potentiostatic mode. While the topic is relevant and contributes to the existing body of knowledge, particularly in the field of material science and surface engineering, the manuscript requires Major Revision before it can be considered for publication. Several aspects of the study, including the methodology, data interpretation, and discussion, need to be enhanced for clarity, accuracy, and depth:
1. The objectives of the study are not explicitly stated in the introduction. The authors should clearly define the research questions or hypotheses they aim to address with this study.
2. What are the specific research questions or hypotheses driving this study? How does this work differentiate itself from previous studies on PEO coatings on AA7075?
3. Include more references that discuss advancements in PEO technology and its application on aluminum alloys: https://doi.org/10.1016/j.matpr.2018.04.177; https://doi.org/10.3390/coatings11010004. This will help situate your work within the current state of research.
4. The description of the PEO process parameters is somewhat generic. The authors need to provide more detailed justification for selecting specific voltages (425 and 450 V), pulse frequency, and duty cycle. What preliminary studies or literature reviews were conducted to determine these parameters?
5. There is insufficient information on the reproducibility of the experiments. The study would benefit from a statistical analysis of the coating thickness, porosity, and corrosion resistance data.
6. The manuscript lacks quantitative analysis regarding surface morphology. The authors mention the presence of "pancake-like" and "nodular" structures but do not quantify the distribution or size of these features across different samples. The authors must provide a more quantitative analysis of the surface morphology, including the size distribution of pores and nodules.
7. Consider using image analysis software to quantify the distribution and size of surface features. This could provide more insight into how the voltage affects surface morphology.
8. How do the differences in surface morphology and coating thickness between samples at 425 V and 450 V correlate with their corrosion resistance? Are there any specific microstructural features that enhance or impair corrosion resistance?
9. What are the potential mechanisms behind the observed differences in coating performance at varying voltages? How do these findings align or contrast with existing literature on PEO coatings for aluminum alloys?
10. Revise typo errors in the reference list, particularly subscripts in the chemical formulas in Ref #27, etc.
Comments on the Quality of English LanguageThe manuscript would benefit from a thorough review of language and grammatical errors. Consider professional editing to improve clarity and readability.
Author Response
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Round 2
Reviewer 2 Report
Comments and Suggestions for Authors1. Lacks Detailed Methodological Justification
Reviewer Comment: The article does not provide a thorough justification for the chosen experimental parameters, particularly why specific voltages, frequencies, and duty cycles were selected for the PEO process.
Author’s Response in Manuscript: The manuscript mentions, "The duty cycle and frequency was adopted from the studies that explored on the effect of corrosion behavior at different duty cycle and frequency for PEO coating" (p. 3). It does not, however, go into great depth as to why the precise figures of 425 V, 450 V, 1000 Hz, and 80% duty cycle were selected over alternative options. This lack of detailed justification remains a gap, as the manuscript does not connect these parameters to their expected impact on the results in a detailed manner.
2. Insufficient Data on Initial Surface Quality
Reviewer Comment: The study inadequately details the initial surface quality and preparation of the AA7075 substrates before the PEO process.
Author’s Response in Manuscript: The revised manuscript now includes the following detail: "Prior to the PEO treatment, substrates were ground and polished using silicon carbide papers at 240 -1200 grit size, then ultrasonically washed in acetone, ethanol, and deionized water for 10 mins. Substrates were subsequently acid pickled in nitric acid dip (500 mL 67% HNO3 in 1L distilled water) for 3 mins, then rinsed with DI water and air dried" (p3). This additional information provides a clearer understanding of the substrate’s initial condition, adequately addressing the concern.
3. Overlooks Long-Term Durability Insights
Reviewer Comment: The article fails to address the long-term durability and performance of the PEO-coated AA7075 beyond the initial corrosion tests.
Author’s Response in Manuscript: The manuscript remains focused on the results of short-term corrosion tests, stating, "Potentiodynamic polarization and EIS analyses show the improved corrosion resistance of the PEO-coated samples compared to the bare AA7075" (p. 13). However, there is no discussion or data on long-term durability or performance under prolonged exposure to environmental conditions, leaving this concern unaddressed.
4. Neglects Environmental Impact Assessment
Reviewer Comment: The research does not evaluate the environmental impact of using PEO-coated AA7075.
Author’s Response in Manuscript: There is no mention or discussion of the environmental impact of the PEO coating process or its sustainability benefits in the revised manuscript. The Introduction (p. 1) and Conclusion (p. 14) sections do not address potential environmental benefits, such as reducing corrosion-related failures and maintenance, leaving this concern unaddressed.
5. Inadequate Comparative Analysis
Reviewer Comment: The article does not provide a robust comparative analysis between PEO-coated AA7075 and other surface treatment methods.
Author’s Response in Manuscript: The manuscript discusses the corrosion behavior of the PEO-coated samples but lacks a detailed comparison with other coating methods. For example, the "Results and Discussions" section (p. 9) primarily focuses on comparing the performance of the PEO-coated samples at different voltages but does not compare these results to other surface treatments such as anodizing or traditional coatings. This limits the ability to assess the relative advantages or disadvantages of PEO coatings.
Comments on the Quality of English LanguageNot required
Author Response
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Reviewer 5 Report
Comments and Suggestions for AuthorsMost of Reviewer #3's comments have been addressed, which I appreciate. However, some issues remain unresolved:
1. For comment 3, while the authors added related sentences, they did not include the recommended references in my review report.
2. Another concern is the limited number of references in the introduction. The authors cited only 13 sources in the literature review, which is insufficient. For instance, reference #8 is repeatedly cited across several sections: lines 43-49, lines 50-54, lines 70-72, lines 74-76, and lines 81-83. Given the extensive research on the electrical parameters of PEO coatings in recent years, the introduction and literature review are still inadequate.
3. On page 2, in the last paragraph, the reference for the work by Azghandi et al. is missing.
Author Response
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