Optimization of the Corrosion Resistance of Electroless Ni–W–P Coatings on Magnesium Alloys by the Response Surface Methodology

Round 1

Reviewer 1 Report

The paper contains very interesting results. Nevertheless, the manuscript should be rewrite and improved to be published. Some of the observations and comments that they influenced my decision are the following:

1. In Introduction section some specific information about the domains where can be used this alloy deposited with the proposed coating.
2. Th following sentence do not have scientific background: “However, the corrosion resistance of magnesium and its alloys is extremely poor”. There are a lots of corrosion experiments on Mg alloys. Moreover, in the papers mentioned at this statement as reference, the word “magnesium” or “Mg” are missing.
3. Should be added in manuscript the method used to determinate the chemical composition of the alloy.
4. Is mentioned in manuscript that the alloy was washed by deionized water. Wy authors do not skip this step or replace with other media keeping in mind that Mg alloys are very reactive at contact with aqua solutions?
5. The equipment used for corrosion test should be added. Also, the manufacturer can be added. The components of corrosion cell used in experiments should be added (keeping in mind that the potential was reported to SHE).
6. Why the coating was heat-treated?
7. Some graphics have poor quality and are hard to understand.
8. Both graphs from Fig. 5-7 should be identify in figure caption.
9. There are a lot of discussions about the corrosion resistance and the parameters used for orthogonal experimental design but is not a discussion about the importance of value of potential in open circuit (electrode potential) and time of immersion. So, in these discussions to what parameters/ is referring the authors when they mention the corrosion resistance?
10. At the 3.4 section there are some discussion about some important electrochemical parameters, but they are not described (only abbreviated). Moreover, is not any information about them or the method used to extract/identify. Which was the immersion time (OCP monitoring) before to start the polarization resistance test? I think that is in strongly relationship with your initial tests where the electrode potential was monitoring.
11. The EIS experiments/results are missing.
12. In Conclusions the following finding can be found: “electroless-plated layer possessed a uniformly dense structure”. What is the scientific support of this statement and where can it be found in the manuscript?

Author Response

Response letter

Dear referees and editor:

We are very pleasure to receive the comments about our manuscript (No.1005177 ). The manuscript has been revised according to the suggestion of referees. The change of the revised manuscript has been highlighted with a red font.

1、In Introduction section some specific information about the domains where can be used this alloy deposited with the proposed coating.

Thanks for your suggestion, the manuscript has been revised in page 1. 

2、Th following sentence do not have scientific background: “However, the corrosion resistance of magnesium and its alloys is extremely poor\ There are a lots of corrosion experiments on Mg alloys. Moreow, in the papers mentioned at this statement as reference, the word “magnesium” or "Mg” are missing.

Thanks for your suggestion, the manuscript has been revised in page 1. 

3、Should be added in manuscript the method used to determinate the chemical composition of the alloy.

Thanks for your suggestion, the chemical composition and surface morphology of the coating alloy are analyzed by SEM and EDS, the results added in Figure 10. 

4、Is mentioned in manuscript that the alloy was washed by deionized water. Wy authors do not skip this step or replace with other media keeping in mind that Mg alloys are very reaction at contact with aqua solutions?

Thanks for your suggestion, the experimental results showed that magnesium alloy will not react with deionized water in a short period of time , this operation is to obtain the cleanness of magnesium alloy surface. It is advantageous to the coating formed on magnesium alloy surface.

5、The equipment used for corrosion test should be added. Also, the manufacturer can be added. The components of corrosion cell used in experiments should be added (keeping in mind that the potential was reported to SHE).

Thanks for your suggestion, the manuscript has been revised in page 3.

 6、Why the coating was heat-treated?

Thanks for your suggestion, Through heat-treated release coating  internal stress, avoid coating crack due to excessive internal stress.  

7、Some graphics have poor quality and are hard to understand.

Thanks for your suggestion.

8、Both graphs from Fig. 5-7 should be identify in figure caption.

Thanks for your suggestion.

9、There are a lot of discussions about the corrosion resistance and the parameters used for orthogonal experimental design but is not a discussion about the importance of value of potential in open circuit (electrode potential) and time of immersion. So, in these discussions to what parameters/ is referring the authors when they mention the corrosion resistance?

Thanks for your suggestion. Because the Ni-W-P alloy is passive material, magnesium alloy is active material, so use the OCP characterization of coating corrosion resistance_.

10、At the 3.4 section there are some discussion about some important electrochemical parameters, but they are not described (only abbreviated). More over, is not any information about them or the method used to extract/identify. Which was the immersion time (OCP monitoring) before to start the polarization resistance test? I think that is in strongly relationship with your initial tests where the electrode potential was monitoring.

Thanks for your suggestion. In this work, use the OCP characterization of coating corrosion resistance, the OCP is an independent test.

11、The EIS experiments/results are missing.

Thanks for your suggestion, the impedance spectroscopy was not tested in this work, and the manuscript has revised.

12、In Conclusions the following finding can be found: Kelectroless-plated layer possessed a uniformly dense structure”. What is the scientific support of this statement and where can it be found in the manuscript?

Thanks for your suggestion, the coating surface morphology added in Figure 10, the result showed that Ni-W-P coating possessed a uniformly dense structure.

Reviewer 2 Report

The methodology applied in the manuscript „Optimization of the Corrosion Resistance of Electroless Ni-W-P Coatings on Magnesium Alloys by the Response Surface Methodology“ by B. Liu et all is interesting for scientists as well as for technologists. The applied methodology could accurately predict optimal process parameters and thus shorten the time required to optimize the experimental parameters.

Although Mg-alloy and Ni-W-P coating were used in the paper, the principle is also applicable to other technologically important materials and alloys.

Generally, the manuscript is well-written, but there are some missing data. Therefore, I recommend a major revision of the manuscript.

Remarks:

1. General remark: It would be useful to cite some recent references and extending the introduction part to complete the state of the art of the paper.
2. Introduction part: For wider scientific audience it would be useful to describe the response surface method (RSM) in more detail.
3. Experimental part: page 2, lines 72-79: The text is related to the alloy surface treatment procedure. Time of the activation procedure???Experimental parameters of the electroless plating process should be described in detail. For example, time, concentrations, temperature ….
4. Experimental part: pages 2-3, lines 80-86: corrosion test: A corrosion cell (electrodes, counter, reference, working; electrolyte …should be mentioned in the text. The impedance spectroscopy was mentioned in the text. Where were the results presented/displayed?
5. Page 3, line 86:…..”potential amplitude =” ± 5 mV and frequency range between 10⁵ and 10^-2 Hz.
6. Figure 1, page 3: Please check the values of the (OCP) potentials! mV or V?

Author Response

Dear referees and editor:

We are very pleasure to receive the comments about our manuscript (No.1005177 ). The manuscript has been revised according to the suggestion of referees. The change of the revised manuscript has been highlighted with a red font.

1、General remark: It would be useful to cite some recent references and extending the introduction part to complete the state of the art of the paper.

Thanks for your suggestion, the impedance spectroscopy was not tested in this work, and the manuscript has revised.

2、Introduction part: For wider scientific audience it would be useful to describe the response surface method (RSM) in more detail.

Thanks for your suggestion, the response surface method (RSM) information was introduced in more detail, and the manuscript has revised.

3、Experimental part: page 2, lines 72-79: The text is related to the alloy surface treatment procedure. Tme of the activation procedure???Experimental parameters of the electroless plating process should be described in detail. For example, time, concentrations, temperature ....

Thanks for your suggestion, the impedance spectroscopy was not tested in this work, and the manuscript has revised.

4、Experimental part: pages 2-3, lines 80-86: corrosion test: A corrosion cell (electrodes, counter, reference, working; electrolyte ...should be mentioned in the text. The impedance spectroscopy was mentioned in the text. Where were the results presented/displayed?

Thanks for your suggestion, the impedance spectroscopy was not tested in this work, and the manuscript has revised.

5、Page 3, line 86:..…,Jpotential amplitude =H ± 5 mV and frequency range between 105 and 10"2 Hz.

Thanks for your suggestion, the impedance spectroscopy was not tested in this work, and the manuscript has revised.

6、Figure 1, page 3: Please check the values of the (OCP) potentials! mV or V?

Thanks for your suggestion, the Figure 1 has revised. 

Round 2

Reviewer 1 Report

Unfortunately, the authors did not take act of my previous review. I am deeply saddened that the effort of a reviewer is not appreciated, and the observations and comments are treated superficially. Even so, below you can find my observations.  

1. Not any specific application of coatings on Mg alloy was mention or highlighted (just a general remark).
2. Probably, my observation about the references for “However, the corrosion resistance of magnesium and magnesium alloys is extremely poor in aqueous solution and the atmospheric environment ^{[7, 8]}” are not understood. There are a lots of corrosion tests of Mg alloys published. Furthermore, the references 7 and 8 do not have any relation with the authors’ remark. In those articles there is nothing related to Mg alloys.
3. Regarding my previous third comment “Should be added in manuscript the method used to determinate the chemical composition of the alloy” the authors added in manuscript something else.
4. The alloy reacts with aquas solution undoubtedly. Probably, in the first moments the kinetics is slowly… Nevertheless, some experiments must be done to draw a conclusion.
5. Regarding my 5^th comment from R1, the authors did not respond adequately and the manuscript has not been amended accordingly (the components of corrosion cell, the reference electrode used, …).
6. At least the words “right” and “left” should be found in figures caption for better identification!
7. The answer to my 9^th comment from R1 fails from scientific point of view!
8. The OCP can be an independent experiment but the to make potentiodynamic polarization experiments have also need OCP monitoring first … Further, the main electrochemical parameters are not explained, the method used for identifying and the experimental procedure are not described …
9. In the SEM image from Fig.10 can be noted only the morphological features of coating and not “uniformly dense structure”.

Author Response

Dear editor:

  We are very pleasure to receive the comments about our manuscript (No.1005177 ). The manuscript has been revised R2 according to the suggestion of referees. The change of the revised manuscript has been highlighted with a red font.

1. Not any specific application of coatings on Mg alloy was mention or highlighted (just a general remark).

Ni-W-P alloy coating has excellent wear resistance and corrosion resistance, in the preparation of the coating on magnesium alloy surface can overcome the low hardness , prone to corrosion of magnesium alloys weaknesses, broadening the scope of the application of magnesium alloys in marine atmosphere environment.

2. Probably, my observation about the references for “However, the corrosion resistance of magnesium and magnesium alloys is extremely poor in aqueous solution and the atmospheric environment ^{[7, 8]}” are not understood. There are a lots of corrosion tests of Mg alloys published. Furthermore, the references 7 and 8 do not have any relation with the authors’ remark. In those articles there is nothing related to Mg alloys.

Thank you for your reminding，the references 7 and 8 have revised.

3. Regarding my previous third comment “Should be added in manuscript the method used to determinate the chemical composition of the alloy” the authors added in manuscript something else.

The magnesium alloy chemical composition tested by inductively coupled plasma spectrometer (ICP)，and revised in manuscript.

4. The alloy reacts with aquas solution undoubtedly. Probably, in the first moments the kinetics is slowly… Nevertheless, some experiments must be done to draw a conclusion.

Thank you very much for your attention. This work uses immersion test to carry out OCP test of the Ni-W-P coating, measuring the time when the OCP drops rapidly to negative value, to determine the corrosion resistance of the coating. The corresponding time is the failure time of the coating showed in figure 1. 

5. Regarding my 5^th comment from R1, the authors did not respond adequately and the manuscript has not been amended accordingly (the components of corrosion cell, the reference electrode used, …).

Thank you for your reminding，the information of corrosion cell have revised in manuscript.

6. At least the words “right” and “left” should be found in figures caption for better identification!

Thank you for your suggestion，I have revised in manuscript.

7. The answer to my 9^th comment from R1 fails from scientific point of view!

Because the OCP of magnesium alloy is more lower than the Ni-W-P alloy, once the coating loses its protective effect on magnesium alloy, intense hydrogen evolution reaction occurs in contact with aqueous solution, and the OCP drops rapidly. Therefore, the rapid change of OCP of the coating can be used to determine whether the coating has lost its protective effect on magnesium alloy. And it revised in manuscript.

8. The OCP can be an independent experiment but the to make potentiodynamic polarization experiments have also need OCP monitoring first … Further, the main electrochemical parameters are not explained, the method used for identifying and the experimental procedure are not described …

Thank you for your reminding, and I have revised in manuscript.

9. In the SEM image from Fig.10 can be noted only the morphological features of coating and not “uniformly dense structure”.

Thank you very much for your attention. In order to characterize the uniformly dense structure of the coating more accurately, I added the cross-section morphology of the coating, and the results showed that there are no obvious defects in coating, which provided effectively protection of magnesium alloy.

Reviewer 2 Report

The manuscript (coatings-1005177) can be accepted for publication in the present form.

Best regards.

Author Response

Dear editor:

  Thanks for your help, welcome to Harbin Engineering University.

Round 3

Reviewer 1 Report

There are a lots of corrosion tests of Mg alloys published. Furthermore, the updated references 7 and 8 are published in 2003 and 1987 and cannot sustain the authors affirmation.

Author Response

Dear reviewer，

    Thank you for your suggestion，I have completed the revision of references 7 and 8，these references sustain the affirmation that "the corrosion resistance of magnesium and magnesium alloys is extremely poor in aqueous solution and the atmospheric environment ".

Best regards,

Your's 

Liu Bin