Optimization of Plasma Electrolytic Oxidation Technological Parameters of Deformed Aluminum Alloy D16T in Flowing Electrolyte

Round 1

Reviewer 1 Report

In the article under consideration, the authors set the task of optimizing the PEO process for the formation of an oxide coating on aluminum.

Notes:

1. In the abstract, the authors state that they "have developed a cationic-alkaline electrolyte", although this type of electrolyte has been used in a large number of works.

2. The Introduction gives the impression of a simple enumeration of a large number of works, i.e. compilation without deep analysis. The authors approached the issue of PEO approximately by citing work 90. At the same time, a large number of citations have a very weak relation to the stated subject of research. It is striking that a third of all citations, many of which are only very indirectly related to PEO, are citations of the works of the authors themselves or their co-authors in previous works: more than 20 citations of articles by L.Ropyak, more than 15 - by I.Shatskyi. The authors were so carried away by the pursuit of quantity that they even put citations 195 and 196 (lines 154 and 155), which are not in the bibliography. At the same time, in recent years, a large number of works have been published directly related to the analysis of the PEO process on aluminum, the mechanism of formation of a ceramic coating, and a detailed study of its composition, structure, and morphology. These are well-known and widely discussed articles by many authors: C.Blawert, S.V.Lamaka, M.L.Zheludkevich, A.Sobolev, M.Mohedano, E.Matykina, B.Mingo, A.Rogov, A.Yerokhin, A.Matthews and others.

3. Section 1.2, called "Microscopic Studies" by the authors, presents the results of several experiments carried out using an optical microscope, SEM and XRD. It is very difficult to assess their significance, the reproducibility of the results is not shown. Even more important than what has been said is that, unfortunately, there is no serious analysis of the results obtained.

4. The authors mention in the Introduction and in the Results section the importance of studying the corrosion resistance of the coating and even cite literature sources (106,107,138), but no attempt is made to evaluate this important characteristic.

5. The authors use the standard method of experiment planning to optimize the technological parameters of PEO. They built response surfaces and the results are shown in Table 5. Apparently, this is what they call "construction of a mathematical model of the process"? However, the data given in Tables 5 and 6 are surprising - the authors really insist on the reality of such a number of digits obtained after the dot in the parameter values: 18.56169; 10.59442; 119.5216…?

6. The results of the planning of the experiment, apparently, can have a certain practical significance. However, in general, the presented work, unfortunately, does not add significant scientific knowledge to the understanding of the PEO process and to the possibility of reasonable control of this technological process.

Author Response

Comments and Suggestions for Authors

In the article under consideration, the authors set the task of optimizing the PEO process for the formation of an oxide coating on aluminum.

Notes:

1. 1.In the abstract, the authors state that they "have developed a cationic-alkaline electrolyte", although this type of electrolyte has been used in a large number of works.

Response 1

The authors selected the optimal component composition of the aqueous electrolyte potassium hydroxide (KOH) and sodium silicate (Na₂SiO₃), current density, flow rate, and temperature of the electrolyte for PEO aluminum alloy D16T, which provide maximum microhardness , minimum wear , and minimum cone-likeness ceramic coating.

2.The Introduction gives the impression of a simple enumeration of a large number of works, i.e. compilation without deep analysis. The authors approached the issue of PEO approximately by citing work 90. At the same time, a large number of citations have a very weak relation to the stated subject of research. It is striking that a third of all citations, many of which are only very indirectly related to PEO, are citations of the works of the authors themselves or their co-authors in previous works: more than 20 citations of articles by L.Ropyak, more than 15 - by I.Shatskyi. The authors were so carried away by the pursuit of quantity that they even put citations 195 and 196 (lines 154 and 155), which are not in the bibliography. At the same time, in recent years, a large number of works have been published directly related to the analysis of the PEO process on aluminum, the mechanism of formation of a ceramic coating, and a detailed study of its composition, structure, and morphology. These are well-known and widely discussed articles by many authors: C.Blawert, S.V.Lamaka, M.L.Zheludkevich, A.Sobolev, M.Mohedano, E.Matykina, B.Mingo, A.Rogov, A.Yerokhin, A.Matthews and others.

Response 2

 Corrected. We reduced the text of the Introduction and and the total number of citations, including citations of authors and co-authors, have been shortened. We deleted quote [90] (line 108) on page 3; fixed errors on page 4 in the numbering of quotations: line 154 [94,95,96,118,195], deleted [195]; line 155 should be [119], but not [196]; line 162 [127,118], deleted [118]; lines 167-174 were deleted (repetition of the lines 175-177 and lines 162-165), and other edits were made to improve the manuscript (See article).

We know articles on PEO written by many authors: C. Blawert, S.V. Lamaka, M.L. Zheludkevich, A. Sobolev, M. Mohedano, E. Matykina, B. Mingo, A. Rogov, A. Yerokhin, A. Matthews and others. We added relevant citations related to the description of the PEO process and regimes [55], [80], the use of ceramic coatings for the protection of cast aluminum alloys for high-temperature [89] and the optimization of PEO processes [94], [95]:

[55] Mohedano, M.; Lu, X.; Matykina, E.; Blawert, C.; Arrabal, R.; Zheludkevich, M.L. Plasma electrolytic oxidation (PEO) of metals and alloys. In Encyclopedia of Interfacial Chemistry: Surface Science and Electrochemistry. Wandelt, K., Eds.; Elsevier: Amsterdam, Netherlands, 2018; pp. 423–438. https://doi.org/10.1016/B978-0-12-409547-2.13398-0.

[80] Rogov, A.B.; Huang, Y.; Shore, D.; Matthews, A.; Yerokhin, A. Toward rational design of ceramic coatings generated on valve metals by plasma electrolytic oxidation: The role of cathodic polarisation. Ceramics International 2021, 47, 34137–34158. https://doi.org/10.1016/j.ceramint.2021.08.324.

[89] Shirani, A.; Joy, T.; Rogov, A.; Lin, M.; Yerokhin, A.; Mogonye, J.-E.; Korenyi-Both, A.; Aouadi, S.M.; Voevodin, A.A.; Berman, D. PEO-Chameleon as a potential protective coating on cast aluminum alloys for high-temperature applications. Surface and Coatings Technology 2020, 397, 126016. https://doi.org/10.1016/j.surfcoat.2020.126016.

[94] Matykina, E.; Arrabal, R.; Skeldon, P.; Thompson, G.E. Optimisation of the plasma electrolytic oxidation process efficiency on aluminium. Surface and Interface Analysis 2010, 42, 221–226. https://doi.org/10.1002/sia.3140.

[95] Vakili-Azghandi, M.; Fattah-alhosseini, A.; Keshavarz, M.K. Optimizing the electrolyte chemistry parameters of PEO coating on 6061 Al alloy by corrosion rate measurement: Response surface methodology. Measurement 2018, 124, 252259. https://doi.org/10.1016/j.measurement.2018.04.038.

3. Section 1.2, called "Microscopic Studies" by the authors, presents the results of several experiments carried out using an optical microscope, SEM and XRD. It is very difficult to assess their significance, the reproducibility of the results is not shown. Even more important than what has been said is that, unfortunately, there is no serious analysis of the results obtained.

Response 3

Added. Figure 6 and Figure 7 are combined into one:

Figure 6. SEM micrograph of the interface between PEO coating and the base alloy D16T (a) and the EDS analysis of the PEO coating: (b)—area of EDS analysis; (c)—resulting spectrum and chemical composition at the analyzed area.

The mechanism of formation of PEO coatings on aluminum alloys is described in publications [55,56,57,58].

4. The authors mention in the Introduction and in the Results section the importance of studying the corrosion resistance of the coating and even cite literature sources (106,107,138), but no attempt is made to evaluate this important characteristic.

Response 4

This article does not aim to investigate the corrosion resistance of PEO coatings on D16T aluminum alloy. The authors investigated the influence of technological parameters of the PEO process (C, i, v, and T) on microhardness , wear , and cone-likeness. In their further research, the authors plan to optimize the PEO process to ensure maximum corrosion resistance of D16T aluminum alloy in typical aggressive environments.

5. The authors use the standard method of experiment planning to optimize the technological parameters of PEO. They built response surfaces and the results are shown in Table 5. Apparently, this is what they call "construction of a mathematical model of the process"? However, the data given in Tables 5 and 6 are surprising - the authors really insist on the reality of such a number of digits obtained after the dot in the parameter values: 18.56169; 10.59442; 119.5216…?

Response 5

Corrected in Table 5, Table 5 and the text of the article reduced the number of digits after the period.

6.The results of the planning of the experiment, apparently, can have a certain practical significance. However, in general, the presented work, unfortunately, does not add significant scientific knowledge to the understanding of the PEO process and to the possibility of reasonable control of this technological process.

Response 6

The obtained regression equations (4), (5), (6) make it possible to estimate the influence of the component composition of the silicate-alkaline electrolyte and the technological regimes of the PEO aluminum alloy D16T in the flowing electrolyte (C, i, v, and T), respectively, on the microhardness , wear , and cone-likeness  of parts with coatings and contribute to a deeper understanding of the mechanism of formation of ceramic oxide coatings and the influence of PEO process parameters on the operational properties of ceramic coatings and the possibility of conducting reasonable management of this PEO technological process.

The team of authors express their gratitude to the reviewer for valuable recommendations that have been taken into account to improve significantly the quality of this paper.

Author Response File: Author Response.docx

Reviewer 2 Report

This study aims to optimize the technological process of PEO treatment on aluminum alloys in the flowing electrolyte. This study achieves certain originality but is insufficient for acceptance in as-received form. I think that this study should be improved in these aspects:

1. The Introduction part is too long and there are too many references in this study. In my opinion, these paragraphs from “Design methods include the selection of rational forms of parts from aluminum alloys [17, 18],…” to “During operation, they provide for the justification of safe modes of operation of aluminum parts [72,73], the use of specialized anti-vibration devices [74,75,76], the use of monitoring of operational damage to coatings [77,78,79]” can be deleted.

2. In Introduction part, the authors give one of PEO advantages, environmental friendliness. Authors should add some recent works about environmental friendly methods or technologies on PEO treatment. For example, Jin Qin, Xiaoting Shi, Hongyu Li, et al., Performance and failure process of green recycling solutions for preparing high degradation resistance coating on biomedical magnesium alloys, Green Chemistry, 2022, 24, 8113-8130. Moreover, the application areas of PEO treatment should be introduced and some works should be added. In fact, besides aluminum alloys, PEO treatment, an effective surface treatment method, is widely used to improve the property of magnesium alloy (for example, Xiaoting Shi, Yu Wang, Hongyu Li, et al, Corrosion resistance and biocompatibility of calcium-containing coatings developed in near-neutral solutions containing phytic acid and phosphoric acid on AZ31B alloy, Journal of Alloys and Compounds, 2020, 823, 153721). In addition, other papers have also studied the influences of electrical parameters on property of anodic coatings developed on aluminum alloys, for example, X.J. Li, M.Zhang, S.Wen, X.Mao, et al., Microstructure and wear resistance of micro-arc oxidation ceramic coatings prepared on 2A50 aluminum alloys, Surf. & Coat. Technol., 2020, 394: 125853.

3. The reason why the flowing electrolyte was adopted in this study should be given.

4. In p4, the words from Line 167 to Line 169 were almost the same as those from Line 175 to Line 177.

5. Figure 6 should be combined with Figure 7 into one figure.

6. In some part of this study, one paragraph only includes three sentences (Lines 342-344, 350-352, p9), which should be revised. Each paragraph should have certain length.

Author Response

Comments and Suggestions for Authors

This study aims to optimize the technological process of PEO treatment on aluminum alloys in the flowing electrolyte. This study achieves certain originality but is insufficient for acceptance in as-received form. I think that this study should be improved in these aspects:

1. The Introduction part is too long and there are too many references in this study. In my opinion, these paragraphs from “Design methods include the selection of rational forms of parts from aluminumalloys [17, 18],…” to “During operation, they provide for the justification of safe modes of operation of aluminum parts [72,73], the use of specialized anti-vibration devices [74,75,76], the use ofmonitoring of operational damage to coatings [77,78,79]” can be deleted.

Response 1

Corrected. We reduced the text of the Introduction and and the total number of citations, including citations of authors and co-authors, have been shortened. We deleted quote [90] (line 108) on page 3; fixed errors on page 4 in the numbering of quotations: line 154 [94,95,96,118,195], deleted [195]; line 155 should be [119], but not [196]; line 162 [127,118], deleted [118]; lines 167-174 were deleted (repetition of the lines 175-177 and lines 162-165), and other edits were made to improve the manuscript (See article).

2. In Introduction part, the authors give one of PEO advantages, environmental friendliness. Authors should add some recent works about environmental friendly methods or technologies on PEO treatment. For example, Jin Qin, Xiaoting Shi, Hongyu Li, et al., Performance and failure process of green recycling solutions for preparing high degradation resistance coating on biomedical magnesium alloys, Green Chemistry, 2022, 24, 8113-8130. Moreover, the application areas of PEO treatment should be introduced and some works should be added. In fact, besides aluminum alloys, PEO treatment, an effective surface treatment method, is widely used to improve the property of magnesium alloy(for example, Xiaoting Shi, Yu Wang, Hongyu Li, et al, Corrosion resistance and biocompatibility of calcium-containing coatings developed in near-neutral solutions containing phytic acid and phosphoric acid on AZ31B alloy, Journal of Alloys and Compounds, 2020, 823, 153721). In addition, other papers have also studied the influences of electrical parameters on property of anodic coatings developed on aluminum alloys, for example, X.J. Li, M.Zhang, S.Wen, X.Mao, et al., Microstructure and wear resistance of micro-arc oxidation ceramic coatings prepared on 2A50 aluminum alloys, Surf. & Coat. Technol., 2020, 394: 125853.

Response 2

Considered. We included in the citations the recommended articles on the environmental friendliness of the PEO process [59], the use of PEO for magnesium alloy [65], and the influence of the electrical parameters of the PEO process on the properties of cladding coatings on aluminum alloys [79], [80]:

[59] Qin, J.; Shi, X.; Li, H.; Zhao, R.; Li, G.; Zhang, S.; Ding, L.; Cui, X.; Zhao, Y.; Zhang, R. Performance and failure process of green recycling solutions for preparing high degradation resistance coating on biomedical magnesium alloys. Green Chemistry 2022, 24, 8113–8130. https://doi.org/10.1039/D2GC02638D.

[65] Shi, X.; Wang, Y.; Li, H.; Zhang, S.; Zhao, R.; Li, G.; Zhang, R.; Sheng, Y.; Cao, S.; Zhao, Y.; Xu, L.; Zhao, Y. Corrosion resistance and biocompatibility of calcium-containing coatings developed in near-neutral solutions containing phytic acid and phosphoric acid on AZ31B alloy. Journal of Alloys and Compounds 2020, 823, 153721. https://doi.org/10.1016/j.jallcom.2020.153721.

[79] Li, X-J.; Zhang, M.; Wen, S.; Mao, X.; Huo, W-G.; Guo, Y-Y.; Wang, Y-X. Microstructure and wear resistance of micro-arc oxidation ceramic coatings prepared on 2A50 aluminum alloys. Surface and Coatings Technology 2020, 394, 125853. https://doi.org/10.1016/j.surfcoat.2020.125853.

[80] Rogov, A.B.; Huang, Y.; Shore, D.; Matthews, A.; Yerokhin, A. Toward rational design of ceramic coatings generated on valve metals by plasma electrolytic oxidation: The role of cathodic polarisation. Ceramics International 2021, 47, 34137–34158. https://doi.org/10.1016/j.ceramint.2021.08.324.

3. The reason why the flowing electrolyte was adopted in this study should be given.

Response 3

The authors were unable to find in the literature the results of studies of the PEO process of D16T aluminum alloy in a flowing electrolyte.

Conducting PEO in the flowing electrolyte has the following advantages:

Supply of "fresh" electrolyte to the reaction zone is ensured;

The intensity of gas removal increases;

The physical and mechanical properties of the ceramic coating are improved (microhardness  and wear );

The accuracy of the shape of parts with an oxide coating (cone-likeness) increases.

4. In p4, the words from Line 167 to Line 169 were almost the same as those from Line 175 to Line 177.

Response 4

Corrected. See point 1.

5. Figure 6 should be combined with Figure 7 into one figure.

Response 5

Figure 6 and Figure 7 are combined into one:

Figure 6. SEM micrograph of the interface between PEO coating and the base alloy D16T (a) and the EDS analysis of the PEO coating: (b)—area of EDS analysis; (c)—resulting spectrum and chemical composition at the analyzed area.

6. In some part of this study, one paragraph only includes three sentences (Lines 342-344, 350-352, p9), which should be revised. Each paragraph should have certain length.

Response 6

Corrected. Lines 342-352 on page 9 combined into one paragraph and supplemented (microhardness , wear , and cone-likeness)       (C, i, v, and T).

The team of authors express their gratitude to the reviewer for valuable recommendations that have been taken into account to improve significantly the quality of this paper.

Author Response File: Author Response.docx

Reviewer 3 Report

1. I have seen too many citations used in the manuscript, especially in the introduction. Besides, many of them were used as blocks.  of course, block quotations are acceptable, but it's important for authors to be selective about their use. It is recommended to remove those that are not directly related to the manuscript.

2. There are a total of 138 references in the manuscript, please check the following citations: [195], [196] on page 4, lines 7-8.

3. Although the introduction is very long, some of the information given in the introduction is not compatible with the content of the manuscript. For example, coating thickness measurement was mentioned in the introduction, methods, and abstract, but I could not see any results regarding the issue in the results and discussions. 

Author Response

Comments and Suggestions for Authors

1. I have seen too many citations used in the manuscript, especially in the introduction. Besides, many of them were used as blocks.  of course, block quotations are acceptable, but it's important for authors to be selective about their use. It is recommended to remove those that are not directly related to the manuscript.

Response 1

Corrected.

2. There are a total of 138 references in the manuscript, please check the following citations: [195], [196] on page 4, lines 7-8.

Response 2

Corrected. We reduced the text of the Introduction and and the total number of citations, including citations of authors and co-authors, have been shortened. We deleted quote [90] (line 108) on page 3; fixed errors on page 4 in the numbering of quotations: line 154 [94,95,96,118,195], deleted [195]; line 155 should be [119], but not [196]; line 162 [127,118], deleted [118]; lines 167-174 were deleted (repetition of the lines 175-177 and lines 162-165), and other edits were made to improve the manuscript (See article).

3. Although the introduction is very long, some of the information given in the introduction is not compatible with the content of the manuscript. For example, coating thickness measurement was mentioned in the introduction, methods, and abstract, but I could not see any results regarding the issue in the results and discussions. 

Response 3

Corrected. The thickness of the PEO coatings was 180−210 µm.

The team of authors express their gratitude to the reviewer for valuable recommendations that have been taken into account to improve significantly the quality of this paper.

Author Response File: Author Response.docx

Reviewer 4 Report

The following corrections may be incorporated 

Line no 199 to 207 each point may  begin with uppercase letter

Line no 210 , studied is misspelled as "stidied" , it may  be corrected.

Table 2 , units not properly spelled . it may be properly used

Author Response

Comments and Suggestions for Authors

The following corrections may be incorporated 

Line no 199 to 207 each point may  begin with uppercase letter

Corrected.

Line no 210 , studied is misspelled as "stidied" , it may  be corrected.

Corrected.

Table 2 , units not properly spelled . it may be properly used

Corrected in Table 5, Table 5 and the text of the article the writing of the dimension of the units.

The team of authors express their gratitude to the reviewer for valuable recommendations that have been taken into account to improve significantly the quality of this paper.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Accept

Author Response

The team of authors express their gratitude to the reviewer for valuable recommendations that have been taken into account to improve significantly the quality of this paper.

Reviewer 2 Report

After revision, the manuscript has been improved significantly. However, I think that the paper should be improved in these aspects:

1. There are ten keywords in this study, and some should be deleted.

2. The full name of plasma electrolytic oxidation (PEO) should be consistent in the study, therefore the title of “Optimization of Plasma-Electrolytic Oxidation Technological Parameters of Deformed Aluminum Alloy D16T in Flowing Electrolyte” should be changed into “Optimization of Plasma Electrolytic Oxidation Technological Parameters of Deformed Aluminum Alloy D16T in Flowing Electrolyte”.

3. The level of English should be further improved. For example, (1) Among a number of strengthening methods, PEO should be singled out, which is intensively developing (“developing” should be changed into “developed”) and is currently one of the most popular, environmentally friendly and fairly cost-effective technologies for forming oxide layers on aluminum and its alloys….(2) The phrase of “Research aim and objectives” in Page 4 should be deleted. (3) The sentence of “The load on the diamond Vickers pyramid was 0.5 N and 1.0 N” should be combined with the phase of “Holding time of 12 s to 15 s” into “The load on the diamond Vickers pyramid was 0.5 N and 1.0 N with the holding time of 12 s to 15 s”. (4) “Accordingly, for the fad and fE degrees of freedom and the level of significance” is not a sentence, and therefore it should be revised. (5) In the sentence of “In the article Premchand, C. et al. [103 138] studied the influence of the ratio of electrolyte components on the corrosion resistance of PEO coatings and found that excellent…..”, “In the article” should be deleted.

Author Response

After revision, the manuscript has been improved significantly. However, I think that the paper should be improved in these aspects:

1. There are ten keywords in this study, and some should be deleted.

Response 1

Corrected.

2. The full name of plasma electrolytic oxidation (PEO) should be consistent in the study, therefore the title of “Optimization of Plasma-Electrolytic Oxidation Technological Parameters of Deformed Aluminum AlloyD16T in FlowingElectrolyte” should be changed into “Optimization of Plasma Electrolytic Oxidation Technological Parameters of Deformed Aluminum Alloy D16T in Flowing Electrolyte”.

Response 2

Corrected. Optimization of Plasma Electrolytic Oxidation Technological Parameters of Deformed Aluminum Alloy D16T in Flowing Electrolyte

3. The level of English should be further improved. For example, (1) Among a number of strengthening methods, PEO should be singled out, which is intensively developing (“developing”should be changed into“developed”) and is currently one of the most popular, environmentally friendly and fairly cost-effective technologies for forming oxide layers on aluminum and its alloys….(2) The phrase of “Research aim and objectives” in Page 4 should be deleted. (3) The sentence of “The load on the diamond Vickers pyramid was 0.5 N and 1.0 N” should be combined with the phase of “Holding time of 12 s to 15 s” into “The load on the diamond Vickers pyramid was 0.5 N and 1.0 N with the holding time of 12 s to 15 s”. (4) “Accordingly, for the fad and fE degrees of freedom and the level of significance” is not a sentence, and therefore it should be revised. (5) In the sentence of “In the article Premchand, C. et al. [103 138] studied the influence of the ratio of electrolyte components on the corrosion resistance of PEO coatings and found that excellent…..”, “In the article” should be deleted.

Response 3

Corrected. See article.

The team of authors express their gratitude to the reviewer for valuable recommendations that have been taken into account to improve significantly the quality of this paper.

Author Response File: Author Response.docx

Reviewer 3 Report

Thanks for the revised manuscript.

Author Response

The team of authors express their gratitude to the reviewer for valuable recommendations that have been taken into account to improve significantly the quality of this paper.