The Influence of Polymeric Sealing Treatment on the Wear Performance of PEO Coating Deposited on AZ31 Mg Alloy

Round 1

Reviewer 1 Report

There are several shortcomings:

1. Please improve the Figure 1a.
2. There is no explanation to why this electrolyte was chosen.
3. There is no explanation to why this polymer was chosen.
4. There is no comparison of polymer application methods and why this method was chosen.
5. For the used experimental and analytic devices. The format should be (type, manufacturer, city, country).
6. EDS mapping on figure 1 has no scale bar.

Comments for author File: Comments.pdf

Author Response

2#

Thank you very much for your kind comments and suggestions, and the point-to-point response areas follows:

• Please improve the Figure 1a.

Answer:We have re-photographed the scanning electron microscope and performed a mapping analysis, which is shown as follow:

10 mm   SEM image	10 mm   Magnesium	Oxygen 10 mm   a   c   b
Carbon 10 mm   d	Aluminium 10 mm   f   e	Zinc

Figure 1. (a) The cross-sectional SEM image of the sealed PEO coating; (b-f) EDS mapping.

 

• There is no explanation to why this electrolyte was chosen.

Answer:During the PEO process, a constant current setting (positive current: 0.4 A and negative current: 0.3 A) was used. The anode was the specimen, and the cathode was a stainless steel plate. The duty cycle and the frequency were 20 % and 2000 Hz, respectively, the PEO treatment time was 4 min. The PEO electrolytic solution and resultant electrical parameters used above can obtain excellent corrosion resistance according to our previous work [10].

 

• There is no explanation to why this polymer was chosen.

Answer:A commercially available DIAMANT Dichtol WFT (1532) type sealant was chosen (main component: ketone), since it is a fast-curing capillary sealer that can impregnate micropores and hairline cracks without the need for vacuum or pressure. Hence, it is commonly applied on to the thermal sprayed coatings, which results in an excellent sealing effect [21]. Furthermore, the sealant infiltrated and cured coating can provide an exceptional chemical as well as temperature resistance. Therefore, in this work, this sealant with ketone as the main component was used to seal the AZ31 Mg-PEO coating having similar pores and cracks as that of the thermal sprayed coatings to some extent. This investigation is mainly intended to explore the effect of sealing treatment on the sliding wear behavior of the AZ31 Mg-PEO coating.

 

• There is no comparison of polymer application methods and why this method was chosen.

Answer:According to the usage guide provided by the sealing agent manufacturer, the sealant was continuously brushed onto the PEO coatings surfaces for 5 min and then dried in the open air. In order to eliminate the influence of the resin layer on the sliding wear process, the coating after sealing treatment was ground on 1000 mesh and 1500 mesh sandpapers in order to ensure that the excess resin layer on the surface of PEO film was completely removed.

 

• For the used experimental and analytic devices. The format should be (type, manufacturer, city, country).

Answer:All the information suggested by reviewer such as type, manufacturer, city and country of the equipments used in this work are added.

 

• EDS mapping on figure 1 has no scale bar.

Answer:We have added the scale bar on them.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Review of Coatings – 1523287

Wang and coauthors report their results on wear resistances before and after applying a polymer solution of Diamant Metallplastic, Dichtol WFT 1532, on PEO coatings of AZ31 alloy workpiece. My recommendation is “Reject” based on the PEO coating quality and the microstructure before and after polymer sealant, not on the wear performance, since I do not have the expertise on surface wear studies.

The weak points of manuscript 1523287;

1) It is evident that the authors have not done a good literature survey on PEO coatings. In literature, studies on PEO coating and its treatment with polymer sealant are known as the studies of duplex coatings. There are at least over 50 papers on the subject of duplex coatings on lightweight metal PEO. The reference section does not mention any one of them.

2) In experimental section: The authors ought to specify the applied electricity parameters: for example, constant current mode or constant voltage mode, or a mixture? if constant current mode, unipolar or bipolar? If bipolar, current density mA dm^-2 for positive/negative polarization. This piece of information is very important for PEO studies.

3) The microstructure image of PEO coating shown (before polymer solution treatment) is poor. I do not think the authors have spent a sufficient amount of time to work on the PEO coating skill. The PEO coating serves as the foundation for the polymer treatment, and its quality shall affect the final results significantly.

Author Response

3#

Thank you very much for your kind comments and suggestions, and the point-to-point response are as follows:

Wang and coauthors report their results on wear resistances before and after applying a polymer solution of Diamant Metallplastic, Dichtol WFT 1532, on PEO coatings of AZ31 alloy workpiece. My recommendation is “Reject” based on the PEO coating quality and the microstructure before and after polymer sealant, not on the wear performance, since I do not have the expertise on surface wear studies.

The weak points of manuscript 1523287;

• It is evident that the authors have not done a good literature survey on PEO coatings. In literature, studies on PEO coating and its treatment with polymer sealant are known as the studies of duplex coatings. There are at least over 50 papers on the subject of duplex coatings on lightweight metal PEO. The reference section does not mention any one of them.

Answer:We have added the typical literature about the PEO coating and its treatment with polymer sealant, which is shown as follow:

There are two kinds of commonly used sealants, namely, organic and inorganic sealants. Organic sealants include epoxy [11-12], polytetrafluoroethylene [13], epoxy-based organosilane [14], octodecylphosphate acid [15], and paraffin wax [16]. The inorganic sealants encompasses silane [12], phosphate, cerium and stannate based salt solutions [15,17]. Sealing treatment process involves brushing [16], soaking [13,15,17], sol-gel infusion [19] and hydrothermal routes [20], etc. Among the many methods, the polymeric sealing treatment is a simple, easy, low cost and effective post coating-treatment to seal the surface of the Mg-based PEO coatings, which can significantly enhance their mechanical and corrosion properties [11,12,16].

[11]  Toorani，M.; Aliofkhazraei, M.; Naderi, R.; et al. Role of Lanthanum Nitrate in Protective Performance ofPEO/Epoxy Double Layer on AZ31 Mg Alloy:Electrochemical and Thermodynamic Investigations[J] Journal of Industrial and Engi-neering Chemistry 53 (2017) 213–227. https://doi.org/10.1016/j.jiec.2017.04.027.

[12]  Toorani, M.; Aliofkhazraei, M.; Mahdavian, M.; et al. Superior corrosion protection and adhesion strength of epoxy coating applied on AZ31 magnesium alloy pre-treated by PEO/Silane with inorganic and organic corrosion inhibitors[J] Corrosion Science 178 (2021) 109065. https://doi.org/10.1016/j.corsci.2020.109065.

[13]  Castellanos, A.; Altube, A.; Vega, J.M.; et al. Effect of different post-treatments on the corrosion resistance and tribological properties of AZ91D magnesium alloy coated PEO[J] Surface & Coatings Technology 278 (2015) 99–107. https:// doi.org/10.1016/j.surfcoat.2015.07.017.

[14]  Ghanbari, A.; Attar, M.M.; A study on the anticorrosion performance of epoxy nanocomposite coatings containing epoxy-silane treated nano-silica on mild steel substrate[J], Journal of Industrial and Engineering Chemistry 23(2015) 145–153. https:// doi.org/10.1016/j.jiec.2014.08.008.

[15]  Mingo, B.; Arrabal, R.; Mohedano, M.; et al. Influence of sealing post-treatments on the corrosion resistance of PEO coated  AZ91 magnesium alloy[J], Applied Surface Science 433(2018)653–667. https://doi.org/10.1016/j.apsusc.2017.10.083.

[16]  Liu, Y.; Wen, S.; Liang, G.; et al. Improvement in corrosion resistance of micro-arcoxidized AZ91 alloy sealed with cement-mixed paraffin wax[J], Journal of materials research and technology 2021;15:6956-6973. https://doi.org/10.1016/j.jmrt.2021.11.088.

 

• In experimental section: The authors ought to specify the applied electricity parameters: for example, constant current mode or constant voltage mode, or a mixture? if constant current mode, unipolar or bipolar? If bipolar, current density mA dm-2 for positive/negative polarization. This piece of information is very important for PEO studies.

Answer:During the PEO process, a constant current setting (positive current: 0.4 A and negative current: 0.3 A) was used. The anode was the specimen, and the cathode was a stainless steel plate. The duty cycle and the frequency were 20 % and 2000 Hz, respectively, the PEO treatment time was 4 min.

 

• The microstructure image of PEO coating shown (before polymer solution treatment) is poor. I do not think the authors have spent a sufficient amount of time to work on the PEO coating skill. The PEO coating serves as the foundation for the polymer treatment, and its quality shall affect the final results significantly.

Answer:We have optimized the PEO process of magnesium alloy and the electrochemical corrosion test results of the micro-arc oxidized AZ31 magnesium alloy after immersion for different times are shown in Figure 1 and Table 1, respectively.

Figure 1 Polarization curve test results of ceramic membranes for different immersion times

 

Table 1 Electrochemical test results of samples immersed for different time after AZ31 substrate and PEO treatment

Samples	Ecorr(V)	Icorr (A/cm2)
AZ31substrate	-1.530	4.516×10-5
PEO-2h	-1.470	2.469×10-8
PEO-24h	-1.422	3.368×10-8
PEO-51h	-1.461	4.021×10-7
PEO-98h	-1.451	4.541×10-6
PEO-148h	-1.476	4.951×10-6

From the Figure 1 and Table 1, it can be found that The PEO film can provide better protection for AZ31 magnesium alloy.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

The results presented in this work could undergo futher evaluation, and this short paper could be considered for publication, but the authors should add a few more words on what is this "polymeric sealant" used for the experiments, and why did you choose this one. Moreover, it is not clear why do you put >>Sead PEO coating<< in Figure 2d, whereas it was "Sealed..." in other sites.

Comments for author File: Comments.pdf

Author Response

Thank you very much for your kind comments and suggestions, and the point-to-point response are as follows:

 

The results presented in this work could undergo futher evaluation, and this short paper could be considered for publication, but the authors should add a few more words on what is this "polymeric sealant" used for the experiments, and why did you choose this one. Moreover, it is not clear why do you put >>Sead PEO coating<< in Figure 2d, whereas it was "Sealed..." in other sites.

Answer:A commercially available DIAMANT Dichtol WFT (1532) type sealant was chosen (main component: ketone), since it is a fast-curing capillary sealer that can impregnate micropores and hairline cracks without the need for vacuum or pressure. Hence, it is commonly applied on to the thermal sprayed coatings, which results in an excellent sealing effect [20]. Furthermore, the sealant infiltrated and cured coating can provide an exceptional chemical as well as temperature resistance. Therefore, in this work, this sealant with ketone as the main component was used to seal the AZ31 Mg-PEO coating having similar pores and cracks as that of the thermal sprayed coatings to some extent. This investigation is mainly intended to explore the effect of sealing treatment on the sliding wear behavior of the AZ31 Mg-PEO coating.

 

“Sead” PEO coating in Figure 2d has been corrected to “Sealed” , which is shown as follow:

 

 

Author Response File: Author Response.pdf

Reviewer 4 Report

Concerning my revision of the paper titled: "The Influence of Polymeric Sealing Treatment on The Wear Performance of PEO Coating Deposited on AZ31 Mg Alloy " coatings-1523287

I have gone through the article. I found that the authors have done good scientific work with new information and provided enough experimental details to reproduce it. So I recommend its publication in the Journal of Coatings after a major revision.

My comments can be summarized as:

 

1. The references need to be updated to 2021.
2. Check the format of reference No. 10; it seems to be different from the others in the reference list.
3. The resolution of Fig. 1 from b to c needs to be better.
4. More comparative studies have to be provided to explore the importance of your work.
5. Please discuss the observations of your work in more detail in the text.
6. Please improve the English language.

Comments for author File: Comments.pdf

Author Response

5#

Thank you very much for your kind comments and suggestions, and the point-to-point response are as follows:

 

I have gone through the article. I found that the authors have done good scientific work with new information and provided enough experimental details to reproduce it. So I recommend its publication in the Journal of Coatings after a major revision.

My comments can be summarized as:

• The references need to be updated to 2021.

Answer: Yes we have updated them.

 

• Check the format of reference No. 10; it seems to be different from the others in the reference list.

Answer: we have updated them.

 

• The resolution of Fig. 1 from b to c needs to be better.
•  

Answer:We have re-photographed the scanning electron microscope and performed a mapping analysis, which is shown as follow:

Figure 1. (a) The cross-sectional SEM image of the sealed PEO coating; (b-f) EDS mapping.

 

 

 

• More comparative studies have to be provided to explore the importance of your work.

Answer: We added some description about the advantages of the sealant used in this work over other sealant. The experimental results also show that this sealant originally used for thermal spray coating can be used for sealing of AZ31 magnesium alloy PEO film, which can significantly increase the sliding war resistance and load-bearing capacity of the film. In addition, we also compared the wear mechanism of the sealed AZ31 Mg-PEO coating with the thermal spray ceramic coating after sealing with an organic sealant in discussion part.

The changed part is as follows:

A commercially available DIAMANT Dichtol WFT (1532) type sealant was chosen (main component: ketone), since it is a fast-curing capillary sealer that can impregnate micropores and hairline cracks without the need for vacuum or pressure. Hence, it is commonly applied on to the thermal sprayed coatings, which results in an excellent sealing effect [21]. Furthermore, the sealant infiltrated and cured coating can provide an exceptional chemical as well as temperature resistance. Therefore, in this work, this sealant with ketone as the main component was used to seal the AZ31 Mg-PEO coating having similar pores and cracks as that of the thermal sprayed coatings to some extent.

There were splats surrounded by large-sized cracks on the wear track of unsealed sample. If the wear process was allowed to continue further, then these isolated splats will get delaminated similar to our observations made on thermal spray coatings [23-24].

 

(5)Please discuss the observations of your work in more detail in the text.

Please improve the English language.

Answer:Dr.Ram has rifined the English language again!

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have responded to all my comments.

Reviewer 2 Report

There are problems with your coating techniques. The quality of your PEO coatings is poor.

Reviewer 4 Report

Dear Editor-in-Chief 
Concerning my revision of the paper titled: "The Influence of Polymeric Sealing Treatment on The Wear Performance of PEO Coating Deposited on AZ31 Mg Alloy " coatings-1523287

The authors have made almost all necessary revisions to the manuscript. So this paper can be published in the Journal without any comments.