Enhancing the Corrosion Resistance of Low Pressure Cold Sprayed Metal Matrix Composite Coatings on AZ31B Mg Alloy through Friction Stir Processing

Round 1

Reviewer 1 Report

In this manuscript, the authors aims to improve the corrosion performance of the low pressure cold sprayed (LPCS) aluminium alloy/alumina metal matrix composite (MMC) coatings on AZ31B magnesium alloy through post surface treatment of friction stir surfacing were examined. This paper is interesting with some novelties, which should be accepted before its accept.

1. The detailed performance of the instrument used in this manuscript should be given.
2. How to evaluate the damage state and load effect? The recent advanced studies on this topic should be referred: 1016/j.ymssp.2021.107774.
3. Which the factor has the most impact on the results? The reason should be explained.
4. The thermal effect of the Friction Stir Processing and has not been introduced. Some recent advanced processes can be referred: 10.1016/j.seta.2021.101183. And some heat process and temperature effect should be referred the paper by searching the keywords on google scholar “Iterative two-layer thermal design strategy ……”;
5. The future study direction should be prospected in Conclusions?
6. The English writing should be improved.

Author Response

RESPONSE TO REVIEWER’S COMMENTS-I

Comment 1

The detailed performance of the instrument used in this manuscript should be given.

Response: As per the reviewer suggestion, the instruments performance was incorporated in the manuscript in Experimental work.

Comment 2

How to evaluate the damage state and load effect? The recent advanced studies on this topic should be referred: 1016/j.ymssp.2021.107774.

Response:

Damage state

The damage states were investigated through Infrared thermal wave technology to estimate the corrosion area and non-corrosion area in the coatings. The damage state of the coating were evaluated through microscopy such as Scanning Electron Microscopy (SEM) and Optical Microscopy (OM). It delivers the coating defects like porosity, oxide inclusion, un melted particles and various features of the coatings.

References:

[i] Jin, G. F., Huang, Z. Y., Zhang, W., Yang, Z. W., & Zhu, L. (2012). Detection and Evaluation of Corrosion Damage under Coating by Infrared Thermal Wave Technology. In Applied Mechanics and Materials (Vol. 190, pp. 447-451). Trans Tech Publications Ltd.

[ii] Nusier, S. Q., Newaz, G. M., & Chaudhury, Z. A. (2000). Experimental and analytical evaluation of damage processes in thermal barrier coatings. International journal of solids and structures, 37(18), 2495-2506.

Load Effect

The load effects were evaluated through vicker hardness tester to estimate the hardness of the coatings. Microhardness measurements were operated by indenting on the metallographic cross sections under 250 g load for 10 s using a Vickers microhardness tester. For each coating sample, the measurement series comprised 15 random indentations. Distance between indentations was kept three times longer than the indentation diagonal to prevent the effects of the stress field of nearby indentations.

Reference:

[i] Wänstrand, O., Larsson, M., & Kassman-Rudolphi, Å. (2000). An experimental method for evaluation of the load-carrying capacity of coated aluminium: the influence of coating stiffness, hardness and thickness. Surface and Coatings Technology, 127(2-3), 107-113

Now the following reference was incorporated as per your comment.

Reference: 

[54] Yang, C. A novel uncertainty-oriented regularization method for load identification.Mech. Syst. Signal. Process. 2021, 158, 107774.

Comment 3

Which the factor has the most impact on the results? The reason should be explained.

Response:

In this investigation, cold spray metal matrix composite coatings were deposited on AZ31B magnesium alloy using optimized variables providing the lowest porosity level and maximum hardness according to the trial and error method. After cold spray, post treatment - friction processing was employed by varying the FSP runs ((1^st,2^nd ,3^rd ).

• Based on the experimental observation it is inferred that the most predominant parameter affect the electrochemical performance of the coating based on FSP runs (1^st , 2^nd and 3^rd ). When comparison of the first and second runs of FSP revealed that the corrosion resistance of the second run was improved due to alumina element refining/redistribution, reduced space between the inter-splat boundary, re-oxidized aluminium phase on the surface, and reduced dislocation density in the matrix phase.
• But at higher runs of FSP (3^rd runs), this difference reduces dramatically, pointing to a loss in corrosion behaviour, because after the 1^st and 2^nd runs, a new layer of surface appears. In that layer, the interface bonding between the alumina particle and the matrix phase is poor and also FSP induce more grain refination with higher frequencies of greater angle grain boundaries. This leads to poor corrosion behaviour on the sample.

Reference:

[1] Hassani-Gangaraj, S.M.; Moridi, A.; Guaglinao, M. Critical review of corrosion protection by cold spray coatings. Surf. Eng. 2015, 31, 803-815.

 Comment 4

The thermal effect of the Friction Stir Processing and has not been introduced. Some recent advanced processes can be referred: 10.1016/j.seta.2021.101183. And some heat process and temperature effect should be referred the paper by searching the keywords on google scholar “Iterative two-layer thermal design strategy ……”;

Response: Thermal effect of the Friction Stir Processing was introduced in the manuscript and and the following references were included in the manuscript.

References:

[55]      Yang, C.; Hou, X.; Chang, S. A synchronous placement and size-based multi-objective optimization method for heat dissipation design on antenna module of space solar power satellite. Sustain. Energy Technol. Assess. 2021, 45, 101183.

[56]      Yang, C.; Hou, X. Iterative two-layer thermal design strategy for step sandwich antenna of space solar power satellite using modified constrained multi-objective optimization. Aerosp. Sci. Technol. 2021, 118, 106987.

Comment 5

The future study direction should be prospected in Conclusions?

Response: The suggestions for future research was incorporated in the conclusion as per your comment.

Comment 6

The English writing should be improved.

Response: Throughout the manuscript the English writing was enhanced.

Author Response File: Author Response.pdf

Reviewer 2 Report

This manuscript reports on Enhancing the Corrosion Resistance of Low Pressure Cold Sprayed Metal Matrix Composite Coatings on AZ31B Mg alloy through Friction Stir Processing. I recommend a major revision, because introduction and discussion parts need significant improvements.

Specific comments referring to parts of the paper, tables or figures.

1. Please rewrite the abstract. In the current form it is not acceptable
2. Please specify and explain novelty of the current study in comparison to previously published manuscripts.
3. Please add information about manufacture of equipment (including city, country) to entire second part of the manuscript.
4. Authors need to provide higher resolution in Fig. 2 because black line between alloy and coating looks like a possible crack. Please add a surface characterization of the coating. Where is the measuring bar in Fig. 2?
5. Why do authors show the indentation morphology in Fig. 3, especially at such a low quality? If they want to show absence of cracks, they should apply significantly higher load (at least HV1).
6. There is no scale bar in the Figure 2.
7. Figure 4 should be deleted or changed since the usage of screenshots of any software is not acceptable. What is about accuracy of such measurements?
8. In Fig. 5 it is difficult to recognize something especially “refination”. Higher additional magnification is required as well as EDS (WDS) measurements. I would also add cross-sections as well. Please check if word “refination” exist.
9. 2. part should be called XRD. Discussion in this part should be improved and expanded. Please explain why peaks shifted to lower angles.
10. Authors should add additional discussion to the entire manuscript.
11. Please check reference list and change according to journal rules.
12. Entire manuscript should be recheck because some words were written with capital letter (like “Techniques” (page 2), double space or dot were used. Furthermore, a lot of mistakes in the manuscript could be found such as „dislotation density” (page 7)

Author Response

RESPONSE TO REVIEWER’S COMMENTS-II

Comments 1

Please rewrite the abstract. In the current form it is not acceptable

Response: Now the abstract is revised as per your suggestion.

Comments 2

Please specify and explain novelty of the current study in comparison to previously published manuscripts.

Response: As per the reviewer comment the novelty of the current study in comparison to previously published work were incorporated in the introduction part of the manuscript.

According to the published literatures [1-53], it is evident that, till date no research was conducted to improving the corrosion performance of magnesium alloy using low pressure cold sprayed metal matrix composite coating by post process treatment.  

Keeping the above point in mind the present investigation was conducted to enhancing the corrosion resistance of low pressure cold sprayed metal matrix composite coatings on AZ31B Mg alloy through friction stir processing.

Comments 3

Please add information about manufacture of equipment (including city, country) to entire second part of the manuscript.

Response: The manufacture of the equipment (Model, Make, and Country) was included in the manuscript 2.Experimental work

Comments 4

Authors need to provide higher resolution in Fig. 2 because black line between alloy and coating looks like a possible crack. Please add a surface characterization of the coating. Where is the measuring bar in Fig. 2?

Response: The resolution in Figure 2 was enhanced also the surface characteristic of the coating was included in 3. Coating Microstructure and characterization. The measuring bar in Figure 2 is included in the manuscript.

Comments 5

Why do authors show the indentation morphology in Fig. 3, especially at such a low quality? If they want to show absence of cracks, they should apply significantly higher load (at least HV1).

Response: Figure 3 is omitted as per your kind perusal.

Comments 6

There is no scale bar in the Figure 2.

Response: Figure 2 is revised with scale bar as per your suggestion.

Comment 7

Figure 4 should be deleted or changed since the usage of screenshots of any software is not acceptable. What is about accuracy of such measurements?

Response: Figure 4 is eliminated in the manuscript as per your recommendation.

Comment 8

In Fig. 5 it is difficult to recognize something especially “refination”. Higher additional magnification is required as well as EDS (WDS) measurements. I would also add cross-sections as well. Please check if word “refination” exist.

Response: The word refination is not exist in the Figure 5. (Now figure 5 is changed as Figure 4). Refination means that the alumina particles entirely get well dispersed into the matrix phase.

Comments 9

2. part should be called XRD. Discussion in this part should be improved and expanded. Please explain why peaks shifted to lower angles.

Response: XRD part is improved and incorporated in the manuscript in Coating Microstructure and characterization. Initially, XRD data show peak shifting to a lower 2θ value, indicating an expansion to a higher lattice parameter.

Comment 10

Authors should add additional discussion to the entire manuscript.

Response: The discussion is elaborated throughout the manuscript

Comment 11

Please check reference list and change according to journal rules.

Response: The references were changed as per the journal format.

Comment 12

Entire manuscript should be recheck because some words were written with capital letter (like “Techniques” (page 2), double space or dot were used. Furthermore, a lot of mistakes in the manuscript could be found such as „dislotation density” (page 7)

Response: As per the reviewer suggestion, whole manuscript was revised.

Author Response File: Author Response.pdf

Reviewer 3 Report

The effect of FSP on the microstructure, mechanical and corrosion resistance of Al-Al2O3 metal matrix composite has been extensively studied [A-C]. I cannot see any novelty in this manuscript to worth its publication. The authors also have not stated the novelty of their work in the introduction of the manuscript.

[A] Using friction stir processing to augment corrosion resistance of cold sprayed AA2024/Al2O3 composite coatings; https://doi.org/10.1016/j.jallcom.2018.09.386

[B] Cold sprayed AA2024/Al2O3 metal matrix composites improved by friction stir processing: Microstructure characterization, mechanical performance and strengthening mechanisms; https://doi.org/10.1016/j.jallcom.2017.11.132

[C] Optimization of cold-sprayed AA2024/Al2O3 metal matrix composites via friction stir processing: Effect of rotation speeds; https://doi.org/10.1016/j.jmst.2018.03.016

Other comments to increase the quality of this manuscript:

• In experimental, how did you calculate the volume percent of Al and Alumina?
• The model of SEM, XRD and other employed devices need to be included in the manuscript.
• What do you mean with the resolution of 0.032 for XRD? Usually, step size and step time are reported to indicate the accuracy of XRD measurement.
• In Figure 2, the labels “a” and “b” should be added. Moreover, a scale need to be added for the optical microscope image.
• Figures 3 and 4 have nothing to show. Why did the authors present them? They must be removed from the manuscript.
• A same parameter (ρ) must be used for dislocation density in table 2 and manuscript. The reference for equations 1 and 2 is required.
• In Figure 6, labels “a” and “b” are required. The title and unit of vertical axis (williamson –Hall graph) are not correct. For xrd graph, if the unit of vertical axis is counts per second, then the values must be shown. The caption also mentioned desolation density which need to be removed.
• E_corr, E_pit, and E_rp are potentials not current densities (page 9 line 9). The current densities should be measured and added to table 3 to indicate the corrosion resistance of the samples.
• The corrosion behavior of the samples have been treated superficially. There are not enough explanation about Figs. 8a-e.
• The English must be substantially improved. The article is full of grammatical and typo errors, which make it difficult to understand its scientific quality.

Author Response

RESPONSE TO REVIEWER’S COMMENTS-III

Comments 1

In experimental, how did you calculate the volume percent of Al and Alumina?

Response:   The volume percent of Al and Alumina estimated using following method

Calculation:

Make a basis of 100cm³ of the final powder mixture

True volume of final powder mixture: 30 gm

Volume of Al alloy powder =80 cm³

Weight of 80 cm3 Al alloy powder =( 80 cm³)(density)

    =80cm³(2.78 gm/cm³)=222.4 gm

Volume of Alumina= 20 cm³

Weight of 20 cm3 Alumina=(20 cm³) (density)

=(20cm³) (3.98gm/cm³)=79.6gm

Total weight of 100cm3 of the final powder mixture=222.4gm+79.6gm=302 gm

Density of the final powder mixture=302gm/100cm³=3.02gm/cm3

Now go back to the powder using the calculated density of the final mixture

True volume of 30 gm final powder mixture=30gm/3.02gm/cm3=9.934 cm3

Then

Volume of Al alloy powder=7.947 cm³

Volume of Alumina powder=1.9868 cm³

Volumetric ratio = 7.947cm3/1.9868 cm³=4/1

Comments 2

The model of SEM, XRD and other employed devices need to be included in the manuscript.

Response: As per the reviewer comments the model of of SEM, XRD and other employed devices were incorporated in the manuscript.

Comments 3

What do you mean with the resolution of 0.032 for XRD? Usually, step size and step time are reported to indicate the accuracy of XRD measurement.

Response: The resolution of the XRD was fixed at 0.032^o  as per the X ray diffractometery specification. It captures the XRD patten with better resolution outcome.

Comments 4

In Figure 2, the labels “a” and “b” should be added. Moreover, a scale need to be added for the optical microscope image.

Response: As per the reviewer comments, in Figure 2 is revised.

Comments 5

Figures 3 and 4 have nothing to show. Why did the authors present them? They must be removed from the manuscript.

Response: As per the reviewer suggestion, the figures 3 and 4 were omitted

Comments 6

A same parameter (ρ) must be used for dislocation density in table 2 and manuscript. The reference for equations 1 and 2 is required.

Response: As per the reviewer comments the same parameter (ρ) was used for dislocation density in table 2 and manuscript. References for equation 1 and 2 were incorporated in the manuscript.

References:

[14]      Yang, K.; Li, W.; Niu, P.; Yang, X.; Xu, Y. Cold sprayed AA2024/Al₂O₃ metal matrix composites improved by friction stir processing: Microstructure characterization, mechanical performance and strengthening mechanisms. J. Alloy. Compd. 2018, 736, 115-123.

[41]      Williamson, G.K.; Hall, W.H. X-ray line broadening from filed aluminium and wolfram. Acta. Metall. 1953, 1, 22-31.

Comments 7

In Figure 6, labels “a” and “b” are required. The title and unit of vertical axis (williamson –Hall graph) are not correct. For xrd graph, if the unit of vertical axis is counts per second, then the values must be shown. The caption also mentioned desolation density which needs to be removed.

Response: As per the reviewer suggestion, the labels “a” and “b” was incorporated in the Figure 6. Williamson –Hall graph and XRD graph was corrected as per your kind information. The caption mentioned in the figure also corrected.  (Now Figure 6 is changed as Figure 5)

Comments 8

Ecorr, Epit, and Erp are potentials not current densities (page 9 line 9). The current densities should be measured and added to table 3 to indicate the corrosion resistance of the samples.

Response: As per the reviewer suggestion the above line was revised and the current densities of the samples was incorporated in table 3.

Comments 9

The corrosion behaviors of the samples have been treated superficially. There are not enough explanation about Figs. 8a-e.

Response: As per the reviewer suggestion the explanation about Figure 8 a-e was revised in section 5. Result and discussion (Now Figure 8 a-e changed as Figure 7 a-e)

Comments 10

The English must be substantially improved. The article is full of grammatical and typo errors, which make it difficult to understand its scientific quality.

Response: The manuscript is revised as per your comment.

Author Response File: Author Response.pdf

Reviewer 4 Report

1. Overall paper is interesting. However, some deficiencies must be improved. The paper is full of grammatical and English-related mistakes. Often, authors use very long sentences up to 3 to 4 lines, making it very difficult to understand the authors’ viewpoint. Figures captions are commonly written as, e.g., Figure 2. Shows the cross…., this is wrong. Just write Figure 2. The cross sectional optical…, no need to say Figure 2 shows the... check figure captions of other published papers. I have highlighted some of English language-related mistakes (tupos, long sentences, etc.) in the attached PDF of the paper.
2. The authors have missed some important literature, e.g. Khodabakhshi, F., et al. “Friction-stir processing of a cold sprayed AA7075 coating layer on the AZ31B substrate: structural homogeneity, microstructures and hardness.” Surface and Coatings Technology331 (2017): 116-128. Also, in the last paragraph of the introduction, elaborate more on what is being conducted in this research than previously reported studies.
3. Which grade of Al alloy was used; authors have only mentioned the composition in the section 2.1.
4. The first sentence of section 2.1 consists of 4.5 lines which is too much long. Sentences longer than 2.5 lines lost their meaningfulness. Use short meaningful sentences.
5. “sandblasting was made through aluminium oxide.” Add the details of sand blasting.
6. How the parameters in Table 1 were selected, please elaborate in the paper.
7. The details of the FSW process are quite vague. For example:
8. What was the hardness of the H13 tool? It should be mentioned.
9. Was the hardness of the H13 tool less or more than the Al2O3 coating.
10. There would definitely be the erosion of the H13 steel from Al2O3, so how the contamination of the surface/coating was avoided from H13 tool material.
11. The parameters of the FSW are not completely described, e.g., how much plunge depth was used?
12. In section 2.2, “porosity of the deposit is measured using optical microscope…” the authors should describe all the sample preparations involved for this step.
13. The figure of the actual setup performing FSW on the sample should be incorporated.
14. The microstructure in Figure 2 is not understandable without a scale. Also, the AZ31B region should be clearly shown in the figure, at the moment it is not clear/focused.
15. Section 3.1 “It is inferred that the greater adhesion occurs between the substrate and coating, no oxidation occurs but metallurgical bonding between the interface of matrix and reinforcement phase is not better.” It is not clear based on what authors are inferring it from the microstructure figure. This must be elaborated in the paper.
16. XRD image in Figure 2 is not discussed
17. Figure 3 is redundant; also it is not focused.
18. In Figure 4, only show the zoomed-in view of the porosity, whereas currently most of the image area is software view, which has no scientific value.
19. “higher rise of FSP runs, the breakage of ceramic particles becoming very lesser.” What do authors mean by higher runs? Did they use run-4 and run-5? If yes, present their results to prove their point; otherwise, this is an overclaim.
20. Contrary to the authors’ claim, Fig.5 c and d do not show the same level of alumina particles dispersal and concentration. Also, if they were almost the same then the result are contradictory to the XRD results in figure 6, where more peaks are detected after run 3.
21. Add explanation why the dislocation density decreases for runs 1 and 2 compared to LPCS sample and then increases for run 3.

Comments for author File: Comments.pdf

Author Response

RESPONSE TO REVIEWER’S COMMENTS-IV

Comment 1

Overall paper is interesting. However, some deficiencies must be improved. The paper is full of grammatical and English-related mistakes. Often, authors use very long sentences up to 3 to 4 lines, making it very difficult to understand the authors’ viewpoint. Figures captions are commonly written as, e.g., Figure 2. Shows the cross…., this is wrong. Just write Figure 2. The cross sectional optical…, no need to say Figure 2 shows the... check figure captions of other published papers. I have highlighted some of English language-related mistakes (tupos, long sentences, etc.) in the attached PDF of the paper.

Response: As per the reviewer suggestion English and grammatical mistakes was revised, All the figure captions were changed as per the reviewer suggestion.

Comment 2

The authors have missed some important literature, e.g. Khodabakhshi, F., et al. “Friction-stir processing of a cold sprayed AA7075 coating layer on the AZ31B substrate: structural homogeneity, microstructures and hardness.” Surface and Coatings Technology331 (2017): 116-128. Also, in the last paragraph of the introduction, elaborate more on what is being conducted in this research than previously reported studies.

Response: As per the reviewer suggestion, the following reference were incorporated  Khodabakhshi, F., Marzbanrad, B., Shah, L. H., Jahed, H., & Gerlich, A. P. Friction-stir processing of a cold sprayed AA7075 coating layer on the AZ31B substrate: structural homogeneity, microstructures and hardness. Surf. Coat. Technol. 2017, 331, 116-128 is added in the manuscript. And in the introduction what is being conducted in the research than the previously reported studies) have been newly incorporated.

According to the published literatures [1-53], it is evident that, till date no research was conducted to improving the corrosion performance of magnesium alloy using low pressure cold sprayed metal matrix composite coating by post process treatment. 

Keeping the above point in mind the present investigation was conducted to enhancing the corrosion resistance of low pressure cold sprayed metal matrix composite coatings on AZ31B Mg alloy through friction stir processing.

Comment 3

Which grade of Al alloy was used; authors have only mentioned the composition in the section 2.1.

Response: AA2024 aluminium alloy was used in this research it was incorporated in the manuscript in the Experimental work.

Comment 4

The first sentence of section 2.1 consists of 4.5 lines which is too much long. Sentences longer than 2.5 lines lost their meaningfulness. Use short meaningful sentences.

Response: As per the reviewer suggestion it is revised in section 2.1 Production of MMC coatings 

Comments 5

“sandblasting was made through aluminium oxide.” Add the details of sand blasting.

Response: Sandblasting (Make Sandstorm, India, Model: SEC-WB-9090) was done with aluminium oxide (grit size of 300 ± 450 µm), morphology :blockish with fine edges, density: 2 g/cm³ and hardness of 3× 10⁴ Megapascal. Now it is incorporated in the Experimental work.

Sandblasting is process of smoothing and cleaning a hard surface by forcing solid particles across that surface at high speeds using compressed air. A sandblasting system includes four basic components: the air source, the sandblasting cabinet, the dust collector, and the blasting media. The air source is usually bottle gas or an air compressor.

Sandblasting can remove paint, rust, and residue from oxidation from materials quickly and efficiently. Sandblasting can also be used to change the condition of a metal's surface, such as through removing scratches or casting marks

Comments 6

How the parameters in Table 1 were selected, please elaborate in the paper.

Response: The selection of optimum cold spray parameters (Table 1) were elaborated in the manuscript. According to the trial and error method and published literature review [1-53] and the cold spray process parameters were optimized. These parameter provide the minimum porosity and maximum hardness to the coating.

References:

[3].       M. Sharifitabar, A. Sarani, S. Khorshahian, M.S. Afarani, Fabrication of     5052Al/Al₂O₃ nanoceramic particle reinforced composite via friction stir processing       route, Mater. Des. 2011, 32, 4164-4172.

[14].     K. Yang, W.Y. Li, P.L. Niu, X.W. Yang, Y.X. Xu, Cold sprayed AA2024/Al₂O₃ metal matrix composites improved by friction stir processing: Microstructure characterization, mechanical performance and strengthening mechanisms, J. Alloy.             Compd. 2018, 736, 115-123

[17].     K. Spencer, D.M. Fabijanic, M.X. Zhang, The use of Al-Al₂O₃ cold spray coatings to       improve the surface properties of magnesium alloys, Surf. Coat. Technol. 2009, 204.      336-344.

[21].     O. Meydanoglu, B. Jodoin, E.S. Kayali, Microstructure, mechanical properties and            corrosion performance of 7075 Al matrix ceramic particle reinforced composite          coatings produced  by the  cold gas dynamic spraying process, Surf. Coat. Technol.         2013,235, 108-116.

[22].     E. Irissou, J.G. Legoux, B. Arsenault, C. Moreau, Investigation of Al-Al₂O₃ cold   spray coating  formation and properties, J. Therm. Spray Technol. 2007,16, 661-668.

[25].     K. Yang, W.Y. Li, C.J. Huang, X.W. Yang, Y.X. Xu, Optimization of cold-sprayed         AA2024/Al₂O₃ metal matrix composites via friction stir processing:  Effect of rotation        speeds, J. Mater. Sci. Technol. 2018, 34, 2167-2177.

[53]        Khodabakhshi, F., Marzbanrad, B., Shah, L. H., Jahed, H., & Gerlich, A. P. Friction-stir processing of a cold sprayed AA7075 coating layer on the AZ31B substrate: structural homogeneity, microstructures and hardness. Surf. Coat. Technol. 2017, 331, 116-128.

Comment 7

The details of the FSW process are quite vague. For example:

Response: As per the reviewer suggestion, FSW process setup and FSP sample is incorporated in the manuscript. In this investigation friction stir welding machine (Make: RV Machine tools, India Model: FSW RL54-090) was utilized as seen in Figure 3. In this equipment H13 steel stir-tool was utilized, The vickers hardnes of the tool is about 510 HV, thread pin with root diameter of 3.3mm, length of 2.8 mm and concave shoulder diameter of 10mm. The stir tool is inclined at 2° elevation angle to eliminate surface flaws. The rotational orientation was counter clockwise at a rotational speed at 800rpm with traverse speed at 40mm/min and plunge depth of 2.8mm to every run of FSP.

Comment 8

What was the hardness of the H13 tool? It should be mentioned.

Response: The Vickers Hardness of the tool is about 510 HV and it is incorporated in the manuscript in the Experimental work.

Comment 9

Was the hardness of the H13 tool less or more than the Al2O3 coating.

Response: From the reviewer comment, the H13 tools (510 HV) have lesser hardness compare to the Al2O3 coatings (1093 HV)

Reference:

 [i] Thirumalaikumarasamy, D., Shanmugam, K., & Balasubramanian, V. (2015). Developing Empirical Relationships to Predict Porosity and Microhardness of Atmospheric Plasma-Sprayed Alumina Coatings on AZ31B Magnesium Alloy. Journal for Manufacturing Science and Production, 15(2), 169-181.

Comment 10

There would definitely be the erosion of the H13 steel from Al2O3, so how the contamination of the surface/coating was avoided from H13 tool material.

Response: As per the reviewer comment the erosion of the H13 steel tool while conducting the experimental it is not avoidable but after FSP the sample is cleaned using acetone to remove the external contamination.

Comment 11

The parameters of the FSW are not completely described, e.g., how much plunge depth was used?

Response: As per the reviewer comment the FSP parameters and the plunge depth  was incorporated in the manuscript Experimental work.

Comment 12

In section 2.2, “porosity of the deposit is measured using optical microscope…” the authors should describe all the sample preparations involved for this step.

Response: As per the reviewer suggestion,

• The optical microscope with an image analysis software was used to analysis the porosity of the coating based on the ASTM B 276 standards.
• For porosity analysis there is no restriction in the sample dimension.
• The sample were metallographically (polishing) processed on the cross section or surface of the coating.
• The polished samples were etched and the etching is used to highlight the, micro structural features or phases present.
• The sample was kept on the optical microscopy to view the micro structural behaviour of the sample.
• By using image analysing software the microstructure of the coating was capture under 900x.
• Using the Metavision software 500 micron square region was chosen on the deposit and the image was examined. The study was repeated five various regions to determine the average percentage level of porosity

Comment 13

The figure of the actual setup performing FSW on the sample should be incorporated.

Response: As per the reviewer suggestion Actual setup of the FSW with FSP samples were added in  Figure 3

Comment 14

The microstructure in Figure 2 is not understandable without a scale. Also, the AZ31B region should be clearly shown in the figure, at the moment it is not clear/focused.

Response: The revised Figure 2 was included in the manuscript.

Comment 15

Section 3.1 “It is inferred that the greater adhesion occurs between the substrate and coating, no oxidation occurs but metallurgical bonding between the interface of matrix and reinforcement phase is not better.” It is not clear based on what authors are inferring it from the microstructure figure. This must be elaborated in the paper.

Response: The section 3.1 was revised as per the reviewer comment.

Comment 16

XRD image in Figure 2 is not discussed

Response: As per the reviewer suggestion Figure 2 XRD image was discussed in the manuscript- Coating Microstructure and characterization

Comment 17

Figure 3 is redundant; also it is not focused.

Response: As per the reviewer suggestion, Figure 3 is omitted.

Comment 18

In Figure 4, only show the zoomed-in view of the porosity, whereas currently most of the image area is software view, which has no scientific value.

Response: As per the reviewer suggestion Figure 4 is omitted

Comment 19

“higher rise of FSP runs, the breakage of ceramic particles becoming very lesser.” What do authors mean by higher runs? Did they use run-4 and run-5? If yes, present their results to prove their point; otherwise, this is an overclaim.

Response: In the manuscript higher run discloses the 3^rd run of FSP. During 3^rd run of FSP the breakage of ceramic particles becoming very lesser. We did not conduct the 4^th  and 5^th  run of FSP.  

Comment 20

Contrary to the authors’ claim, Fig.5 c and d do not show the same level of alumina particles dispersal and concentration. Also, if they were almost the same then the result are contradictory to the XRD results in figure 6, where more peaks are detected after run 3.

Response: In Figure 5 c the particle size of the alumina was small when compare to Figure 5 d. (Now Figure 5 c and d changed as Figure 4 c and d).   In figure 6, The XRD patten of the LPCSed and FSPed samples. The XRD plot reveals the lower size and higher levels of splitting between the alumina elements after FSP. Some of the apex belonging to the alumina elements in the FSPed samples then changed to smaller when compared with the LPCSed sample. More peaks detected after 3rd run of FSP due to alumina particle dispersal does take place better compared with 1^st and 2^nd runs of FSP. (Now Figure 6 is changed as Figure 5).

Comment 21

Add explanation why the dislocation density decreases for runs 1 and 2 compared to LPCS sample and then increases for run 3.

Response: When compared with the LPCSed sample, the dislocation density and micro strain of the FSPed sample were very small. This is owing to the dynamic recrystallisation produced by the stir motion developed through FSP, as evidenced by previous investigations. [42,43]. The fewer dislocation  density  enhances the  corrosion resistance [44,45]. Nevertheless, when MMC coatings are exposed to 3rd run of FSP, higher dislocations are formed with severe micro strains but any non effective breakup of the alumina particles. At 3^rd  run of FSP causes grain refination as well as higher frequencies of greater angle grain boundaries [44, 46], all of which negatively affect corrosion resistance. It is incorpoaretd in the section Williamson-Hall Measurement.

References:

[42]      Zhang, Z.H.; Li, W.Y.; Feng, Y.; Li, J.L.; Chao, Y.J. Global anisotropic response of friction stir welded 2024 aluminum sheets. Acta. Mater. 2015, 92, 117-125.

[43]      Sato, Y.S.; Kokawa, H.; Enomoto, M.; Microstructure evolution of 6063 aluminum during friction-stir welding. Metall. Mater. Trans. A 1999, 30, 2429-2437.

[44]      Rahsepar, M.; Jarahimoghadam, H. The influence of multipass friction stir processing on the corrosion behavior and mechanical properties of zircon-reinforced Al metal matrix composites. Mater. Sci. Eng.  A 2016, 671, 214-220.

[45]      Pandey, V.; Singh, J. K.; Chattopadhyay, K.; Srinivas, N. S.; Singh, V. Influence of ultrasonic shot peening on corrosion behavior of 7075 aluminum alloy. J. Alloy. Compd. 2017, 723, 826-840.

[46]      Sattari, B.; Shamanian, M.; Ashrafi, A.; Salehi, M.; Salimijazi, F. Effect of number of passes on the corrosion behavior of Fe/Al surface composites produced by plasma spraying and friction stir processing. J. Mater. Process. Technol. 2017, 250, 35-44.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The quality of the manuscript has improved somewhat, but the article cannot be published until the following issues are clarified:

• The authors have not provide any answer for my first and most critical comment in first revision:

“The effect of FSP on the microstructure, mechanical and corrosion resistance of Al-Al2O3 metal matrix composite has been extensively studied [A]. I cannot see any novelty in this manuscript to worth its publication. The authors also have not stated the novelty of their work in the introduction of the manuscript, compared with this article for example:

[A] Using friction stir processing to augment corrosion resistance of cold sprayed AA2024/Al2O3 composite coatings; https://doi.org/10.1016/j.jallcom.2018.09.386

• The structure of the revised manuscript seems to be weird. The manuscript should have one “experimental section” and one “Result and discussion”. Now, after presenting some results at sections 3 and 4, they provided another “Result and discussion” section.
• How could the authors detect higher levels of splittation between the alumina elements after FSP from XRD patterns?
• This statement is ambiguous “during FSP, aluminium phases re-oxidized on the surface of the FSPed sample, resulting in significant breakage of the oxide layers of the interior coated Al alloy elements and a reduction in protective performance”. How can re-oxidation of aluminum at the surface results in the breakdown of the oxide layers of the interior coated Al alloy elements?
• In conclusion, the inferior corrosion resistance of coating fabricated by 3 passes of FSP is attributed to the “amalgamate action of the enhanced surface state and damaged interfacial at the interior deposits”. But, there is no evidence (in Fig 4 e, for example) to prove this in the manuscript.
• There are still many grammatical and improper words in the manuscript. Some examples are:

“apex” do you mean XRD peaks?

Refination should be replaced by refinement.

“…to its fewer temperature and…”

….. was conducted to improving the corrosion….”

…. estigation was conducted to enhancing the corrosion…”

“According to the published literatures [1-53]…”

Author Response

1. The authors have not provide any answer for my first and most critical comment in first revision:

“The effect of FSP on the microstructure, mechanical and corrosion resistance of Al-Al2O3 metal matrix composite has been extensively studied [A]. I cannot see any novelty in this manuscript to worth its publication. The authors also have not stated the novelty of their work in the introduction of the manuscript, compared with this article for example:

[A] Using friction stir processing to augment corrosion resistance of cold sprayed AA2024/Al2O3 composite coatings; https://doi.org/10.1016/j.jallcom.2018.09.386

Response: First of all, we wish to apologies to reviewer for missing the above question to answer.

The paper titled Using friction stir processing to augment corrosion resistance of cold sprayed AA2024/Al2O3 composite coatings. In this work, they used the high pressure cold spray process with process gas as nitrogen. They improved the corrosion resistance of AA2024-T3 substrate (base material). With process parameter (gas pressure-3Mpa, powder feed rate- 3 rate/rpm, gas temperature-400⁰C and standoff distance-25mm). For friction stir process the rotational speed fixed as 900rpm for all FSP passes.

Comparing with our work we used low pressure cold spray system with processing gas as air. It is very cheap compared to nitrogen. It will reduce the fabrication cost. The major novelty of our work to improve the corrosion performance AZ31B magnesium alloy substrate (base material). With process parameter (Air pressure-12 bar, Powder feed rate- 10 gram/min, Air temperature-500⁰C and Standoff distance-10mm). For friction stir process the rotational speed fixed as 800rpm for all FSP runs.

The need of improving the AZ31B magnesium alloy because it is lightweight structural material for high volume of aerospace and automobile application. Although in certain application magnesium alloy have acceptable surface properties, but the corrosion resistance of the magnesium alloy is poor. To overcome this problem, the current research aims to enhance the corrosion performance of the low pressure cold sprayed (LPCS) aluminium alloy/alumina metal matrix composite (MMC) coatings on AZ31B magnesium alloy through post surface treatment of friction stir processing

The major difference and advantages of our work compared with the above paper [A].The magnesium is lighter than aluminum because its specific weight is only 2⁄3 of aluminum and 1⁄3 of titanium. So it is better replacement for aluminum components in the aerospace industries and the weights of the components were reduced by using improved metal matrix composite coated magnesium alloy.

Reference:

Tan, Jovan, and Seeram Ramakrishna. "Applications of Magnesium and its Alloys: A Review, Appl. Sci. 2021, 11, 6861 (2021).

And in the introduction section the novelties of our work were compared with previous published work were highlighted now.

2. The structure of the revised manuscript seems to be weird. The manuscript should have one “experimental section” and one “Result and discussion”. Now, after presenting some results at sections 3 and 4, they provided another “Result and discussion” section.

Response: The manuscript is revised as per the reviewer comment and it is highlighted. 

3. How could the authors detect higher levels of splittation between the alumina elements after FSP from XRD patterns?

Response: Apologies to the reviewer, through XRD it is not possible to detect higher levels of splittation between the alumina elements after FSP. Now the above line is revised and it is highlighted in the manuscript.

The above line changed as (The XRD plot reveals that some of the peaks belong to the alumina elements in the FSPed samples, which have changed to smaller when compared with the LPCSed sample [40]. This is due to the lower size and higher levels of splittation between the alumina elements after FSP)

4. This statement is ambiguous “during FSP, aluminium phases re-oxidized on the surface of the FSPed sample, resulting in significant breakage of the oxide layers of the interior coated Al alloy elements and a reduction in protective performance”. How can re-oxidation of aluminum at the surface results in the breakdown of the oxide layers of the interior coated Al alloy elements?

Response:  Apologies to the reviewer, the typical error was occurred on the above line. Now the line is revised and highlighted in the manuscript

The above line changed as (during FSP, aluminium phases re-oxidized on the surface of the FSPed sample. At the higher run of FSP (3^rd run), there is significant breakage of the oxide layers of the interior coated Al alloy elements and a reduction in protective performance. Previous investigations have proved the same behaviour [57])

Reference:

[57]      Niu, P.L.; Li,  W.Y.;  Zhang,  Z.H.; Wang,  F.F.;  Feng,  Y.;  Fu,  M. Significant effect of oxide on mechanical properties of friction-stir-welded AA2024 joints, Sci. Technol. Weld. Joi. 2017, 22, 66-70.

5. In conclusion, the inferior corrosion resistance of coating fabricated by 3 passes of FSP is attributed to the “amalgamate action of the enhanced surface state and damaged interfacial at the interior deposits”. But, there is no evidence (in Fig 4 e, for example) to prove this in the manuscript.

Response:  At 3^rd run of FSP the corrosion resistance was reduced as shown in Figure 7e compared with other run of FSP as shown in figure 7(c-d), it is based on the evidence of tafel plot result. The corrosion resistance of the 3^rd run of FSP is poor compared to 2nd run of FSP. Because the corrosion failure arises due to amalgamate action of the enhanced surface state and damaged interfacial at the interior deposits. The same phenomenon was reported by [53]   

Reference:

[53] Khodabakhshi, F.; Marzbanrad, B.; Shah, L.H.; Jahed, H.; Gerlich, A.P. Friction-stir processing of a cold sprayed AA7075 coating layer on the AZ31B substrate: structural homogeneity, microstructures and hardness. Surf. Coat. Technol. 2017, 331, 116-128.

6. There are still many grammatical and improper words in the manuscript. Some examples are:

“apex” do you mean XRD peaks?

Refination should be replaced by refinement.

“…to its fewer temperature and…”

….. was conducted to improving the corrosion….”

…. estigation was conducted to enhancing the corrosion…”

“According to the published literatures [1-53]…”

Response: The manuscript is revised as per the reviewer comment and it is highlighted. 

Author Response File: Author Response.pdf