Influence of Anodizing by Electro-Chemical Oxidation on Fatigue and Wear Resistance of the EV31A-T6 Cast Magnesium Alloy

Round 1

Reviewer 1 Report

There are several electrochemical methods of anodizing light, i.e., Magnesium, alloys for enhancing the wear & corrosion resistance of the alloys.  Among those are the plasma electrolytic oxidation (PEO) and the micro-arc oxidation (MAO) methods.   For instance, the drawback of the PEO method has been reported as the PEO improves the wear and the corrosion resistance of the Mg-alloys, it reduces the fatigue strength, i.e., fatigue endurance limit, of the alloys up to 19-37%.     However, an addition of rare earth (RE) elements, i.e., Nd & Gd, to the Mg-alloys does enhance the fatigue strength of PEO-anodized Mg-alloys as compared to Mg-alloys without the RE elements.   Recently, an improvised method of the PEO has been developed.   The method is commercially available; and called the electro chemical oxidation (ECO).   The ECO is an improvised form of the PEO, in a way that the ECO uses bipolar pulsed DC sources to avoid disruptive plasma discharge effects and provides dense and compact oxide films.

In a serial of separate investigations of the authors [Ref.25, 26, and the current work], both the PEO and ECO methods were applied on a rare earth-containing Mg-alloy such as the EV31A-T6 cast magnesium alloy.   The study was focused on the influence of the PEO and ECO treatments on the wear properties, corrosion resistance, and the fatigue strength of the EV31A-T6 alloy as compared to the untreated alloy.  The EV31A-T6 alloy is commonly used for automotive/motor-sport components that are subjected to dry sliding in a frequent manner against other components made of different materials, i.e., Cr-bearing steels.   The study included microstructure characterizations, wear property examinations, and fatigue tests.

 In general, the results show that the ECO treatment of the EV31A-T6 alloy has enhanced the tribological behavior and the fatigue performance as compared to the PEO treatment to the alloy.   This occurs because the ECO process has Less intense micro arcs, that is normally generated by the ECO discharge regime, than in PEO process.  Consequently, a denser anodized layer formed in PEO-treated EV31A-T6 alloy with less affected, i.e., detrimental defects, substrate than in the PEO-treated EV31A-T6 alloy.  

The following items have to be paid attention to:

1-In the Abstract at line 18, the statement "the RE-containing"

should be written for what is stand for before the abbreviation.

For instance, rare earth (RE)-containing. 

2-At line 40, the statement "Nd and Gd "should be written for what is stand for before the abbreviation.

In my opinion, the submitted article can be accepted for publication after a minor revision and a reduction in size(optional). The outcome of the article is basically a continuation of a serial of technical communications that have been already in literature.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

A major revision needs for this manuscript based on some issues. Other comments could be found as follows,

1)      No abbreviations should be used in the title and keywords.

2)      All keywords should be found in the abstract or the title.

3)      No quantitative results could be seen in the abstract.

4)      The novelty should be highlighted in the abstract, compared to the literature review.

5)      All process parameters need references, for heat treatments and others.

6)      What was the repeatability of fatigue testing? What was the loading case and condition? It is not clear.

7)      The etchant needs a reference.

8)      Based on data in Table 3, it is not clear how the fatigue strength was obtained. Was it the staircase method or others?

9)      What was the change in the fracture behavior in PEO and ECO?

10)  What are the results for PEO in Figure 5?

11)  What is the standard deviation for the distance in Figure 6? It has no meaning. The standard deviation should be only reported for the hardness.

12)  What is the repeatability of testing in Figure 7(a)? The mean CoF should be reported with the standard deviation.

13)  What is the SEM image for PEO in Figure 11? What is the change in the fracture behavior and the damage mechanism?

14)  The discussion on obtained results for fatigue testing should be extended. They must be compared to other results of other articles.

15)  No references could be found for 2022. They must be updated based on recent articles, published in 2017-2022.

16)  What is the fatigue lifetime for all samples?

17)  The present structure is confusing. All samples should be defined in a table to know which samples were tested and evaluated in this study and which one was from the literature. Names of samples should be defined in a table. Then, all results should be presented for all samples, and not in my case study or one material. It is so confusing to trace the results and the performance of ECO, compared to PEO.

18)  What is the difference between this manuscript and the following articles?

*Influence of Anodization on the Fatigue and Corrosion-Fatigue Behaviors of the AZ31B Magnesium Alloy

*Influence of Anodization on the Fatigue and Corrosion-Fatigue Behaviors of the AZ31B Magnesium Alloy

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Review for

coatings-2118651

Influence of anodizing by electrochemical oxidation (ECO) on fatigue and wear resistance of the EV31A-T6 cast magnesium alloy

The authors present an interesting work about ECO coating of the fatigue and wear properties of EV31 Mg alloy. Albeit this work is in good shape, I think, nonetheless, that the manuscript could be improved if the authors could address the comments and recommendations I listed below.

Figure 2: Please mention in the figure title to indicate a light rubbing on figures a,b. Additionally, you may need to have a top view of PEO coating for a better comparision.

Figure 3: You may need to label the thickness of the coating.

Line 143: Typo ","

Your work is interesting but lacks a comparison of some morphology characterizations. You may need to present more comparisons between the ECO coating and the PEO coating in Figures 8, and 10. Then you can say ECO coating is better. 

I'm very interested in the corrosion properties of this special ECO coating. Will you be about to perform a simple EIS or potentiodynamic test?

Significance :

. The scientific content of this paper is correct. 

. The technical quality of this paper is correct. 

Scientific soundness :

. The subject addressed in this paper is relevant. 

Interest to the readers :

. In my opinion, the method of this paper seems to be interesting for the readership of the journal.  

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Almost all comments were addressed in the revised article. However, it still needs a minor revision, as follows,

1) "Mpa" should be changed to "MPa".

2) More details about the staircase method should be added to the research method.

3) The authors mentioned that "No differences in fracture behavior and damage mechanism were found for PEO and ECO coatings". This issue should be clarified in detail and the physical reason should be described. 

4) The answer to the last comment about the difference between this manuscript and the mentioned references should be added to the text, especially when the novelty is mentioned. 

Author Response

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Author Response File: Author Response.pdf