Study on the Mechanism of CNTs Regulating the Microstructures and Properties of Al–Cu–Mg Alloy

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Please see the file attached.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer:

On behalf of all the contributing authors, I would like to express our sincere appreciations of your letter and reviewers’ constructive comments concerning our article entitled " Study on the Mechanism of CNTs Regulating the Microstruc-tures and Properties of Al-Cu-Mg Alloy " (Manuscript No: crystals-2805457). These comments are all valuable and helpful for improving our article. Point-by-point responses to the nice reviewer are listed below this letter. In this revised version, changes to our manuscript were all highlighted within the document by using red-colored text.

 

Comments 1: The manufacturer of the CNTs used is not named and their characteristics, primarily their dimensions, are not given.

Response: We sincerely appreciate your valuable comments. The CNTs used in this paper are purchased by the SUZHOU TANFENG GRAPHENE TECHNOLOGY Co., Ltd, and the specific size is 5 ~ 50nm.

 

Comments 2: Line 67:《a 1.5 wt.% CNT/Al-Cu-Mg composite was prepare》.

Response: After several groups of experiments in the early stage, the composite material obtained after adding 1.5 wt.% CNTs has the best performance (Ref. 1).

 

Comments 3: Line 159: 3.3. Mechanical Properties and Strengthening Mechanism of the Alloy.

Response: Thanks to the sincere suggestions of the reviewers. In this paper, based on the four strengthening and toughening mechanisms, the effect of CNTs on Al matrix composites is studied. By observing the CNTs and stable dispersion phase in the material, the dislocation movement is inhibited, and the grain boundary is pinned to prevent the recrystallization or growth of the substructure in the matrix, so as to stabilize the microstructure. The purpose of good mechanical properties of Al alloy materials is finally realized by using the load transfer strengthening provided by CNTs.

 

Reference

[1] C. Yuan, Z. Tan, G. Fan, M. Chen, Q. Zheng, Z. Li 2019 Fabrication and mechanical properties of CNT/Al composites via shift-speed ball milling and hot-rolling Journal of Materials Research 34 2609-2619

 

We invited a native English speaker from the United States to help polish our article. We hope that the revised manuscript will be accepted by you. We are very grateful for your advices and contributions to this article. If you have any question about this paper, please don’t hesitate to let us know.

修改后的手稿已重新提交给 Crystals。 我们期待您的早日回复。

此致

通讯作者：

陆莉

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript focuses on the modification of an Al alloy by carbon nanotubes. The results of structural studies and mechanical tests are presented. The level of English is unacceptable. There are many errors in the work. In general, the material presented in the article is not of interest for publication.

I have the following main comments.

1. Line 10 "The effect of CNTs on the modification of α-Al phase was detected by analyzing the XRD results, particularly the inhibition of preferential growth on the (220) crystal plane" The paper does not provide data on "preferential growth on the (220) crystal plane".

2. Line 14 "significant improvements in the tensile strength (480.4 MPa) and yield 14 strength (456.68 MPa) were observed". The paper does not provide any data on what is observed to increase strength.

3. Line 75: "In order to prevent CNTs from transforming into CO2 at high temperature, use the thermodynamic formula...". Where does oxygen come from in aluminum? Why is formula (1) given and what do the parameters used in it mean?

4. Line 78: "it is calculated that when the Al alloy melt is in the semi-solid state" - Where are these calculations given? What is a semi-solid state?

5. Which nanotubes were used in the work?

6. Formula (2) is correct. However, the results obtained in the work are not enough for correct estimates.

7. The hardening effect can be attributed to the formation of Al4C3. However, it is known that the Al - Al4C3 composite degrades rapidly under the influence of atmospheric moisture. Therefore, the results presented in the article are not of interest.

Comments on the Quality of English Language

Obviously, the text of the article was prepared using machine translation. This has led to inadequate translation of technical and scientific terms.

Author Response

Dear Reviewer:

On behalf of all the contributing authors, I would like to express our sincere appreciations of your letter and reviewers’ constructive comments concerning our article entitled " Study on the Mechanism of CNTs Regulating the Microstruc-tures and Properties of Al-Cu-Mg Alloy " (Manuscript No: crystals-2805457). These comments are all valuable and helpful for improving our article. Point-by-point responses to the nice reviewer are listed below this letter.  In this revised version, changes to our manuscript were all highlighted within the document by using red-colored text.

 

Comments 1: Line 10 "The effect of CNTs on the modification of α-Al phase was detected by analyzing the XRD results, particularly the inhibition of preferential growth on the (220) crystal plane" The paper does not provide data on "preferential growth on the (220) crystal plane".

Response: We think this is a good suggestion. Based on the reviewer's comments, we have revised the content of the summary. The changes are as follows:

The purpose of this study was to investigate the effect of carbon nanotube addition on the microstructure and mechanical properties of Al-Cu-Mg alloy composites. By analyzing the XRD results, the extruded and heat-treated composites after the addition of CNTs were preferentially grown on the (220) crystal plane. In addition, the distribution of carbon nanotubes at α-Al grain boundaries was observed by SEM and TEM. The incorporation of carbon nanotubes leads to an increase in the degree of recrystallization in the composite. It is worth noting that based on the study of the four strengthening mechanisms of dislocation strengthening, grain refinement strengthening, load transfer strengthening and second stage strengthening, when the carbon nanotube content is 1.5 wt.%, the tensile strength (480.4 MPa) and yield strength (456.68 MPa) are significantly improved.

 

Comments 2: Line 14 "significant improvements in the tensile strength (480.4 MPa) and yield 14 strength (456.68 MPa) were observed". The paper does not provide any data on what is observed to increase strength.

Response: In terms of the improvement of mechanical properties, we compared with this literature and improved the process (Ref. 1).

 

Comments 3: Line 75: "In order to prevent CNTs from transforming into CO2 at high temperature, use the thermodynamic formula...". Where does oxygen come from in aluminum? Why is formula (1) given and what do the parameters used in it mean?

Response: The oxygen in aluminum is produced in contact with air during the melting process. In order to prevent the decomposition of CNTs and the formation of CO2 with oxygen at high temperature, the formula (1) is given to calculate the optimum addition temperature of CNTs. In the formula, α_Al4C3, α_Al and α_C are the activity of Al4C3, Al and C, respectively, and ΔG is the Gibbs free energy change.

 

Comments 4: Line 78: "it is calculated that when the Al alloy melt is in the semi-solid state" - Where are these calculations given? What is a semi-solid state?

Response: The calculation is given by Formula (1), and the temperature of the melt in the semi-solid state is calculated by combining the formula with the temperature. Semi-solid is the state of the melt in the solid-liquid temperature range.

 

Comments 5: Which nanotubes were used in the work?

Response: Single-walled carbon nanotubes are used in this paper.

 

Comments 6: Formula (2) is correct. However, the results obtained in the work are not enough for correct estimates.

Response: Thanks to the sincere suggestions of the reviewers. In this paper, based on the four strengthening and toughening mechanisms, the effect of CNTs on Al matrix composites is studied. By observing the CNTs and stable dispersion phase in the material, the dislocation movement is inhibited, and the grain boundary is pinned to prevent the recrystallization or growth of the substructure in the matrix, so as to stabilize the microstructure. The purpose of good mechanical properties of Al alloy materials is finally realized by using the load transfer strengthening provided by CNTs.

 

Comments 7: The hardening effect can be attributed to the formation of Al4C3. However, it is known that the Al-Al4C3 composite degrades rapidly under the influence of atmospheric moisture. Therefore, the results presented in the article are not of interest.

Response: Thanks to the sincere suggestions of the reviewers, the formation of carbides at the interface is crucial for the effective load transfer at the strong interface between carbon nanotubes and the matrix (Ref. 2), and the degradation of Al₄C₃ needs to be in a humid environment for a long time, which is very different from the application environment of this composite.

 

Reference

[1] C. Yuan, Z. Tan, G. Fan, M. Chen, Q. Zheng, Z. Li 2019 Fabrication and mechanical properties of CNT/Al composites via shift-speed ball milling and hot-rolling Journal of Materials Research 34 2609-2619

[2] S. Heydari, S.A. Sajjadi, A. Babakhani, H. Eskandari, B. Nateq 2023 An investigation on the effect of Al4C3 on microstructure and mechanical properties of carbon nanotube reinforced aluminum composite Ceramics International 49 14024-14034

 

We invited a native English speaker from the United States to help polish our article. We hope that the revised manuscript will be accepted by you. We are very grateful for your advices and contributions to this article. If you have any question about this paper, please don’t hesitate to let us know.

The revised manuscript has been resubmitted to Crystals. We look forward to your early response.

Yours sincerely,

Corresponding author:

Lu Li

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

The authors carried out research related to the study on the mechanism of CNTs regulating the microstructures and properties of Al-Cu-Mg alloy. The authors carried out different characterizations of the prepared composite materials. Consider that the manuscript could be accepted after carrying out some corrections.

I suggest the authors improve the title of the manuscript. That is, mention in the title the type of nanotube they are using.

Consider that the abstract needs to be rewritten. The authors must highlight their results obtained in their research.

Introduction

I suggest the authors improve the state of the art of the manuscript. The authors mention the use of carbon nanotubes as reinforcing materials. However, they must mention what kind of nanotubes they are using i.e. single layer or multi-layer.

Experimental materials and approach.

Authors must provide a detailed description of the materials they are using in their research.

The authors mention carbon nanotubes as the reinforcing material. They must mention what type of nanotubes they are using, diameters of the nanotubes and how they were obtained or purchased.

The authors should mention the characteristics of the aluminum powder they are using. Particle size distribution. I suggest presenting a picture of the powder used.

Figure 1. Shows the process carried out for the preparation of the composite materials. However, the authors need to provide details of the sample preparation process and their consolidation.

I suggest the authors describe each of the characterization techniques in separate sections. Describe the parameters used in each characterization carried out.

Results.

Consider that the authors should show the microscopy characterization of the raw samples and the heat-treated samples. Show the presence of carbon nanotubes and describe what happens to the carbon nanotubes after the heating process.

Better description of the labels in figure 5 and figure 6.

The authors should improve the description of Figure 7 in the manuscript.

Author Response

Dear Reviewer:

On behalf of all the contributing authors, I would like to express our sincere appreciations of your letter and reviewers’ constructive comments concerning our article entitled " Study on the Mechanism of CNTs Regulating the Microstruc-tures and Properties of Al-Cu-Mg Alloy " (Manuscript No: crystals-2805457). These comments are all valuable and helpful for improving our article. Point-by-point responses to the nice reviewer are listed below this letter.  In this revised version, changes to our manuscript were all highlighted within the document by using red-colored text.

 

Comments 1: About the summary.

Response: We think this is a good suggestion. Based on the reviewer's comments, we have revised the content of the summary. The changes are as follows:

The purpose of this study was to investigate the effect of carbon nanotube addition on the microstructure and mechanical properties of Al-Cu-Mg alloy composites. By analyzing the XRD results, the extruded and heat-treated composites after the addition of CNTs were preferentially grown on the (220) crystal plane. In addition, the distribution of carbon nanotubes at α-Al grain boundaries was observed by SEM and TEM. The incorporation of carbon nanotubes leads to an increase in the degree of recrystallization in the composite. It is worth noting that based on the study of the four strengthening mechanisms of dislocation strengthening, grain refinement strengthening, load transfer strengthening and second stage strengthening, when the carbon nanotube content is 1.5 wt.%, the tensile strength (480.4 MPa) and yield strength (456.68 MPa) are significantly improved.

 

Comments 2: About Introduction.

Response: We sincerely thank the reviewers for their professional advice. Based on the suggestions, we will revise the last paragraph of the introduction. The specific changes are as follows：

In this paper, the recrystallization behavior of CNTs/Al-Cu-Mg composites was studied. The composites were prepared by adding single-walled carbon nanotubes (SWCNTs). The microstructure, test properties and strengthening mechanism of CNTs/Al-Cu-Mg composites were observed and analyzed, and the effect of carbon nanotubes on aluminum composites was revealed.

 

Comments 3: About experimental materials and methods.

Response: Thanks for your suggestion. Based on the suggestions, we will revise the second paragraph of the preparation and process parameters of the pomposite materials. The specific changes are as follows：

A total of 1.5 wt.% CNT/Al-Cu-Mg composite was prepared in a high temperature melting device using industrial pure Al (99.5 wt.%), Al-50 wt.% Cu, Al-10 wt.% Mg and Al-10 wt.% Ti master alloys as raw materials. The CNTs used were purchased by Suzhou Tianfeng GRAPHENE Technology Co., Ltd., with a specific size of 5 ~ 50 nm. The 2024 Al alloy melt was prepared at 800 °C. In order to prevent CNTs from transforming into CO2 at high temperature, use the thermodynamic formula：

                  (1)

 

Comments 4: About Figure 5, Figure 6 and Figure 7.

Response: The following changes were made to the notation of Figures 5 and 6, and to the interpretation of Figure 7:

Figure 5. The element distribution of 1.5 wt.% CNTs/Al-Cu-Mg composites under heat treatment process.

Figure 6. TEM images of 1.5 wt.% CNTs/Al-Cu-Mg composites after heat treatment

The strength of 1.5 wt.% CNTs/Al-Cu-Mg composites in T6 state is shown in Fig-ure 7 and Table 1. The tensile curve strength of the three samples is similar, indicating that the performance of the composite material is stable. The tensile curve shows that the strength of the composites is obvi-ously improved after adding carbon nanotubes, which is due to the fact that carbon nanotubes hinder the movement of dislocations, indicating that CNTs had a significant strengthening effect in Al-Cu-Mg alloy. The tensile strength and elongation were at a stable value, with the highest values reaching 480.4 MPa and 11.91 %, respectively.

 

We invited a native English speaker from the United States to help polish our article. We hope that the revised manuscript will be accepted by you. We are very grateful for your advices and contributions to this article. If you have any question about this paper, please don’t hesitate to let us know.

The revised manuscript has been resubmitted to Crystals. We look forward to your early response.

Yours sincerely,

Corresponding author:

Lu Li

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript has been sufficiently improved to warrant publication in Crystals.

Author Response

Dear Reviewer:

On behalf of all the contributing authors, I would like to express our sincere appreciations of your letter and reviewers’ constructive comments concerning our article entitled " Study on the Mechanism of CNTs Regulating the Microstruc-tures and Properties of Al-Cu-Mg Alloy " (Manuscript No: crystals-2805457). We have partially modified the discussion part of the article. In this revised version, changes to our manuscript were all highlighted within the document by using red-colored text.

Yours sincerely,

Corresponding author:

Lu Li

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have addressed the comments and changes suggested by the reviewers. I consider that the article shows a better structure in the presentation of the results of each of the sections. Therefore, the article can be accepted in its present form.

Author Response

Dear Reviewer:

On behalf of all the contributing authors, I would like to express our sincere appreciations of your letter and reviewers’ constructive comments concerning our article entitled " Study on the Mechanism of CNTs Regulating the Microstruc-tures and Properties of Al-Cu-Mg Alloy " (Manuscript No: crystals-2805457). We have partially modified the discussion part of the article. In this revised version, changes to our manuscript were all highlighted within the document by using red-colored text.

Yours sincerely,

Corresponding author:

Lu Li