Superhydrophobic Corrosion-Resistant Coating of AZ91D Magnesium Alloy: Preparation and Performance
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript “Preparation of superhydrophobic corrosion-resistant coating of AZ91D magnesium alloy and its performance research” by Shucheng Qi et al. describes the approach to modify the surface of the AZ91D magnesium alloy targeted on better protection of the magnesium surface against corrosion. Although the manuscript presents some new data and definitely fits within the scope of the “Coatings”, it cannot be accepted for publication in present state and requires major revision. The comments and questions below should be taken into account when revising the manuscript.
1. It is difficult to read the manuscript because the lingual errors such as inappropriate wording, grammar, and style do not allow the reader to get access to the scientific content of the manuscript and it is recommended first to correct all text. The help of a native speaker is strongly recommended.
2. The authors should carefully check the terminology they use to describe the processes, chemical compounds and other details of their study, and adhere to the well-accepted terms. For example, the term “phosphide” refers to a compound containing the P3− ion or its equivalent, e.g., Zn3P2. The coating discussed in the manuscript contains phosphate, not phosphide. Another example of misused terms is the term “drugs” in line 78 in place of “chemicals”.
3. The introduction of the manuscript should not be restricted with brief discussion of conversion coatings, but also add some description of recent progress in application of superhydrophobic coatings to protect magnesium alloys against corrosion. In this regard, a recent review (doi: 10.1016/j.surfcoat.2024.130607) would be very pertinent.
4. Please carefully check the correspondence between references in the text and those in the references list. For example, the citation to G.Y. Li et al (line 50) should seemingly cite ref. [23], not [21]. There are discrepancies with the references list also for the text “R. Amini and A. A. Sarabi [22]” (line 51) and “Trong-Linh Nguyen et al.[23]” (line 53), as there are no such authors’ names in the whole references list.
5. The term “enhanced surface wettability” (line 58) usually is considered as indication of lower contact angles. The authors wanted to say the opposite.
6. Please specify whether your report the composition of AZ91D alloy (lines 71-73) according to manufacturer data, or determined in this work (by which method and with what accuracy)? Please note also that the total composition presented in the manuscript exceeds 100%.
7. Lines 97-98: “Finally, a composite film layer with superhydrophobic properties was applied to the surface of the magnesium alloy”. Consider replacing “applied to” with “obtained on”.
8. Line 103: “Dataphysicals” should be “Dataphysics”. Please also use similar description style (e.g., brand, model, manufacturer/supplier name, city, country) for all used equipment/substances.
9. Lines 121-123: “This process was repeated three times to calculate the average value. The durability of the composite film under acidic, neutral and alkaline conditions was evaluated by this method.” The above description is vague. What process was repeated 3 times? Were these 3 different specimens of each time submerged for 3 h each or one specimen which was submerged 3 times for 3 h? The average value of what parameter was then determined? Please specify explicitly.
10. Line 126: please provide the manufacturer name for CS2350H electrochemical workstation and the type/version number of software used to analyze the electrochemical data (line 134).
11. Lines 168-169: “The presence of these functional groups provides further evidence for the self-assembly of FAS on the surface of magnesium alloys.” It only confirms the presence of FAS on the surface, not the self-assembly of molecules. Neither it indicates the “homogeneous covering” of the surface (line 172).
12. Lines 173-174: “This layer interacts with the rough micro-nanostructures on the surface and imparts EXCELLENT superhydrophobicity to the sample”. Hardly contact angle of 158° can be qualified as indicative of excellent superhydrophobicity. Compare that with the literature data, e.g. with summarized in abovementioned review (doi: 10.1016/j.surfcoat.2024.130607). You will see that most superhydrophobic coatings for magnesium have contact angles above 160° and even >170°.
13. Figure 4 duplicates the reactions presented in section 3.2. Consider removing it, as it does not give any additional information to the text.
There are many inaccurate phrases which need to be reformulated, e.g.:
14. Lines 180-181: “The ANALYSIS of the growth mechanism of the zinc-based phosphide film IS PRESENTED IN THE PREPARED PHOSPHATE BATH…”
15. Lines 186-187: “The following reaction sequence is observed …” – reactions (5) and (6) are going independently and not in sequence.
16. Lines 195-197: “This compound serves as an initial protective layer, impeding the corrosion of the magnesium alloy substrate and facilitating the growth of the phosphate film, as evidenced by the reaction (9)[35].” Reaction (9) describes the formation of magnesium fluoride and gives NO EVIDENCE of impeding the corrosion or facilitating the growth of the phosphate film.
17. Line 210: Fig. 6 should be Fig. 5.
18. Line 215: “nuclei appeared and grew in the pore region” No pore region was discussed so far. Where is it? Please indicate in SEM images (by arrows, circles or some other means). Also, please add SEM images of the surface before phosphating treatment for the comparison.
19. Lines 215-216, 218: “structure progressively developed”, “steadily expands”, “nearly completely envelops the substrate.” Comparison of Fig5c and Fig5d rather shows opposite: the structure becomes looser.
20. Lines 222-223: “The FAS assembled on the surface of PCC can precisely fill the cracks left after the phosphating reaction.” Fig5e does not support this claim either^ the structure looks even more loose that that in Fig 5d.
21. Line 264, inaccurate phrase “erosion of acid and alkaline solutions”, please consider revision.
23. The phrases in lines 281-282 and 283-284 twice repeat the same claim.
24. Double-check the numbers in the Table 1. The corrosion rate must be proportional to the corrosion current; however, this proportionality is not fulfilled in the table.
25. Line 301 fix the misprint in the word “v50alues”.
26. Line 314, inaccurate phrase “the composite film layer sample is 15 times higher than that of the magnesium alloy substrate.”, please consider revision.
27. Section 3.7 Anti-corrosion mechanism. The analysis in this section is poorly written and does not represent a step ahead, but rather several steps backward. Consider rewriting this section in light of currently established mechanisms of corrosion protection by superhydrophobic coatings.
Comments on the Quality of English Language
English is poor and requires revision.
Author Response
Reviewer #1: The manuscript “Preparation of superhydrophobic corrosion-resistant coating of AZ91D magnesium alloy and its performance research” by Shucheng Qi et al. describes the approach to modify the surface of the AZ91D magnesium alloy targeted on better protection of the magnesium surface against corrosion. Although the manuscript presents some new data and definitely fits within the scope of the “Coatings”, it cannot be accepted for publication in present state and requires major revision. The comments and questions below should be taken into account when revising the manuscript.
- It is difficult to read the manuscript because the lingual errors such as inappropriate wording, grammar, and style do not allow the reader to get access to the scientific content of the manuscript and it is recommended first to correct all text. The help of a native speaker is strongly recommended.
Response: Thank you for pointing out the flaws in the English language. We have double-checked and revised the entire English text!
- The authors should carefully check the terminology they use to describe the processes, chemical compounds and other details of their study, and adhere to the well-accepted terms. For example, the term “phosphide” refers to a compound containing the P3−ion or its equivalent, e.g., Zn3P2. The coating discussed in the manuscript contains phosphate, not phosphide. Another example of misused terms is the term “drugs” in line 78 in place of “chemicals”.
Response: Thanks for the correction. The terminology has been modified by replacing “phosphide” with “phosphate” and “drugs” with “chemicals”. On page 2, line 81.
- The introduction of the manuscript should not be restricted with brief discussion of conversion coatings, but also add some description of recent progress in application of superhydrophobic coatings to protect magnesium alloys against corrosion. In this regard, a recent review (doi: 10.1016/j.surfcoat.2024.130607) would be very pertinent.
Response: Thank you for your suggestion. The manuscript has cited this review (doi: 10.1016/j.surfcoat.2024.130607). On page 1, lines 42-45.
- Please carefully check the correspondence between references in the text and those in the references list. For example, the citation to G.Y. Li et al (line 50) should seemingly cite ref. [23], not [21]. There are discrepancies with the references list also for the text “R. Amini and A. A. Sarabi [22]” (line 51) and “Trong-Linh Nguyen et al.[23]” (line 53), as there are no such authors’ names in the whole references list.
Response: Thank you for the correction. References [21] [22] [23] have been re-cited. On page 2, lines 53-56.
- The term “enhanced surface wettability” (line 58) usually is considered as indication of lower contact angles. The authors wanted to say the opposite.
Response: Thank you for your comment. The term “enhanced” has been changed to “weakened”. On page 2, line 61.
- Please specify whether your report the composition of AZ91D alloy (lines 71-73) according to manufacturer data, or determined in this work (by which method and with what accuracy)? Please note also that the total composition presented in the manuscript exceeds 100%.
Response: Thank you for pointing out the issue. It is stated in the manuscript that the composition of the AZ91D alloy is based on data provided by the manufacturer and that the total composition has been corrected. On page 2, lines 74-76.
- Lines 97-98: “Finally, a composite film layer with superhydrophobic properties was applied to the surface of the magnesium alloy”. Consider replacing “applied to” with “obtained on”.
Response: Thank you for your suggestion. In the manuscript, the words “applied to” have been replaced by “obtained on”. On page 3, line 101.
- Line 103: “Dataphysicals” should be “Dataphysics”. Please also use similar description style (e.g., brand, model, manufacturer/supplier name, city, country) for all used equipment/substances.
Response: Thank you for your suggestion. “Dataphysicals” has been changed to “Dataphysics”. A similar descriptive style has been used, with city, country added after “Dataphysics”. On page 3, lines 107-108.
- Lines 121-123: “This process was repeated three times to calculate the average value. The durability of the composite film under acidic, neutral and alkaline conditions was evaluated by this method.” The above description is vague. What process was repeated 3 times? Were these 3 different specimens of each time submerged for 3 h each or one specimen which was submerged 3 times for 3 h? The average value of what parameter was then determined? Please specify explicitly.
Response: Thank you for pointing out the issue. It has been stated in the manuscript that it is 3 immersions of each sample for 3 hours each. On page 3, line 127
- Line 126: please provide the manufacturer name for CS2350H electrochemical workstation and the type/version number of software used to analyze the electrochemical data (line 134).
Response: Thank you for your suggestion. The name of the manufacturer of the CS2350H electrochemical workstation and the software used to analyze the electrochemical data have been provided in the manuscript. On page 4, lines 131 and 139.
- Lines 168-169: “The presence of these functional groups provides further evidence for the self-assembly of FAS on the surface of magnesium alloys.” It only confirms the presence of FAS on the surface, not the self-assembly of molecules. Neither it indicates the “homogeneous covering” of the surface (line 172).
Response: Thank you for pointing out the issue. The description in the manuscript has been corrected to “further evidence of FAS covering the surface of magnesium alloys”.On page 5, lines 173-174.
- Lines 173-174: “This layer interacts with the rough micro-nanostructures on the surface and imparts EXCELLENT superhydrophobicity to the sample”. Hardly contact angle of 158° can be qualified as indicative of excellent superhydrophobicity. Compare that with the literature data, e.g. with summarized in abovementioned review (doi: 10.1016/j.surfcoat.2024.130607). You will see that most superhydrophobic coatings for magnesium have contact angles above 160° and even >170°.
Response: Thank you for pointing out the issue. After a careful reading of this review (doi: 10.1016/j.surfcoat.2024.130607), we have corrected the description in the manuscript. On page 5, lines 177-178.
- Figure 4 duplicates the reactions presented in section 3.2. Consider removing it, as it does not give any additional information to the text.
There are many inaccurate phrases which need to be reformulated, e.g.:
Response: Thank you for your suggestion. The original Figure 4 has been deleted and some phrases have been rephrased.
- Lines 180-181: “The ANALYSIS of the growth mechanism of the zinc-based phosphide film IS PRESENTED IN THE PREPARED PHOSPHATE BATH…”
Response: Thank you for pointing out the issue. The description in the manuscript has been corrected to read the growth process. On page 6, line 183.
- Lines 186-187: “The following reaction sequence is observed …” – reactions (5) and (6) are going independently and not in sequence.
Response: Thank you for pointing out the issue. The description of this part of the manuscript has been improved. On page 7, lines 189-190.
- Lines 195-197: “This compound serves as an initial protective layer, impeding the corrosion of the magnesium alloy substrate and facilitating the growth of the phosphate film, as evidenced by the reaction (9)[35].” Reaction (9) describes the formation of magnesium fluoride and gives NO EVIDENCE of impeding the corrosion or facilitating the growth of the phosphate film.
Response: Thank you for raising the flaws. The manuscript has been amended for this part of the description. On page 7, lines 199-200.
- Line 210: Fig. 6 should be Fig. 5.
Response: Thank you for pointing out the issue. This issue has been corrected in the manuscript.
- Line 215: “nuclei appeared and grew in the pore region” No pore region was discussed so far. Where is it? Please indicate in SEM images (by arrows, circles or some other means). Also, please add SEM images of the surface before phosphating treatment for the comparison.
Response: Thank you for raising the flaws. The pore zone is not discussed in this paper. The description of this section in the manuscript has been corrected. On pages 7-8, lines 214-216.
- Lines 215-216, 218: “structure progressively developed”, “steadily expands”, “nearly completely envelops the substrate.” Comparison of Fig5c and Fig5d rather shows opposite: the structure becomes looser.
Response: Thank you for pointing out the issue. This figure has been corrected in the manuscript. On page 8, line 224.
- Lines 222-223: “The FAS assembled on the surface of PCC can precisely fill the cracks left after the phosphating reaction.” Fig5e does not support this claim either^ the structure looks even more loose that that in Fig 5d.
Response: Thank you for pointing out the issue. The narrative on this part has been corrected in the manuscript. On page 8, line 224.
- Line 264, inaccurate phrase “erosion of acid and alkaline solutions”, please consider revision.
Response: Thank you for your suggestion. The phrase “erosion of acid and alkaline solutions” has been changed to “corrosion of acid and alkaline solutions” in the manuscript. On page 10, line 263
- The phrases in lines 281-282 and 283-284 twice repeat the same claim.
Response: Thank you for your suggestion. This duplication in the manuscript has been corrected. On page 11, lines 284-285
- Double-check the numbers in the Table 1. The corrosion rate must be proportional to the corrosion current; however, this proportionality is not fulfilled in the table.
Response: Thank you for pointing out the issue. We have checked and corrected the numbers in Table 1. On page 11
- Line 301 fix the misprint in the word “v50alues”.
Response: Thank you for pointing out the issue. This word has been corrected in the manuscript. On page 11, line 300
- Line 314, inaccurate phrase “the composite film layer sample is 15 times higher than that of the magnesium alloy substrate.” please consider revision.
Response: Thank you for pointing out the issue. Phrase “the composite film layer sample is 15 times higher than that of the magnesium alloy substrate” has been changed to “the charge transfer resistance of the composite film layer samples is 15 times higher than that of the magnesium alloy matrix” in the manuscript. On page 12, lines 312-314
- Section 3.7 Anti-corrosion mechanism. The analysis in this section is poorly written and does not represent a step ahead, but rather several steps backward. Consider rewriting this section in light of currently established mechanisms of corrosion protection by superhydrophobic coatings.
Response: Thank you for raising the flaws. Based on the superhydrophobic coatings established so far, we have seriously rewritten the section on anti-corrosion mechanisms, located on page 13.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors1) The authors should provide further details on XPS measurements: scanning rate, software used for peak analysis, etc
2) Uncertainty values should be added for the contact angle results reported
3) A more quantitative correlation between the surface morphology of the different treatments (roughness, surface coverage) and the contact angles observed should be provided
4) The authors should calculate the corrosion inhibition efficiency with respect to uncoated surfaces. See a seminal paper for example, A. Kokalj et al., Simplistic correlations between molecular electronics properties and inhibition efficiencies: Do they really exist? Corrosion Science 179, 108856 (2021)
5) The model proposed and displayed in Figure 12 should be correlated to specific experimental results, which is not the case
6) Have the authors carried out SEM of the surfaces after corrosion? This would be convenient
Author Response
Reviewer#2:
1) The authors should provide further details on XPS measurements: scanning rate, software used for peak analysis, etc
Response: Thank you for your suggestion. XPS scan rates have been added to the manuscript as well as peak analysis software. On page 3, lines 155-156.
2) Uncertainty values should be added for the contact angle results reported
Response: Thank you for pointing out the issue. This part of the manuscript has been added to the water contact angle image. On page 9, line 241.
3) A more quantitative correlation between the surface morphology of the different treatments (roughness, surface coverage) and the contact angles observed should be provided
Response: Firstly, thank you for your suggestion. Secondly, I'm so sorry, our group's research on this small portion of the study is not yet mature enough, but we will put it into our next paper to delve deeper.
4) The authors should calculate the corrosion inhibition efficiency with respect to uncoated surfaces. See a seminal paper for example, A. Kokalj et al., Simplistic correlations between molecular electronics properties and inhibition efficiencies: Do they really exist? Corrosion Science 179, 108856 (2021)//
Response: Thank you for your suggestion. Based on the literature you provided, we have calculated the corrosion inhibition efficiency relative to an uncoated surface. Located on page 11, line 291.
5) The model proposed and displayed in Figure 12 should be correlated to specific experimental results, which is not the case
Response: Thank you for pointing out the issue. The model presented in Figure 12 and the narrative in the manuscript have been corrected to correlate with specific experimental results. On pages 12-13.
6) Have the authors carried out SEM of the surfaces after corrosion? This would be convenient
Response: Thank you for your suggestion. This section is the focus of our team's research for our next paper, so we will publish it in our next post.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe revision made by the authors has improved the manuscript. In present state, the manuscript deserves publication in Coatings.
Comments on the Quality of English LanguageIt would be beneficial to further improve English; nevertheless, in the present state the main ideas and results in general can be assessed properly by readers.
Author Response
Response: Thank you for your suggestion. We reviewed and revised the manuscript for word expression as well as grammar!
Reviewer 2 Report
Comments and Suggestions for AuthorsSome of the changes mentioned by the authors are not obvious in the revised manuscript. For instance, I do not see corrosion inhibition efficiency values nor a valid reference added to refer to the calculations
Author Response
Response: Thank you for your suggestion. We have cited references and calculated the corrosion inhibition efficiency and the results are placed in Table 1. On page 11， lines 277-280.
