Numerical Simulation of the Thermo-Mechanical Behavior of 6061 Aluminum Alloy during Friction-Stir Welding

Round 1

Reviewer 1 Report

INTEREST:

The authors present an interesting study about the simulation of the thermomechanical behavior of 6061 aluminum alloy during the Friction Stir Welding (FSW) process, by means of a finite-element model. The paper is well written and organized. Also, the results are interesting and present some advances and good scientific contributions. In addition, the work provides information of interest to the readers of the “Journal of Manufacturing and Materials Processing” (and also to the materials and welding communities), so I recommend the paper for publication after minor revisions.

 

COMMENTS:

Some points for the authors to consider:

 

1.    Please remove "…The introduction should briefly place the study in a broad context and highlight why it is important. It should define the purpose of the work and its significance. The current state of the research field should be carefully reviewed and key publications cited. Please highlight controversial and diverging hypotheses when necessary. Finally, briefly mention the main aim of the work and highlight the principal conclusions. As far as possible, please keep the introduction comprehensible to scientists outside your particular field of research. References should be numbered in order of appearance and indicated by a numeral or numerals in square brackets—e.g., [1] or [2,3], or [4–6]. See the end of the docu-37 ment for further details on references... " at the beginning of the intro section.

2.    In the experimental part of the manuscript, the authors mention that several welding tests were carried out at different combinations of tool rotation and translation rates. So I would like to know if there was any attempt to verify (or validate) the values predicted by the finite-element model. For example, for me, it is not clear whether the authors checked if the width of the deformation in a real FSW joint, in fact, reaches ~20-60 mm, thus significantly exceeding the stir zone size.  As the work deals with simulation, I believe this is an important issue and the authors should comment on the validity of their simulated data.

3.    In addition, provide recommendations for future research which could advance the state of the art of FSW welding simulation.

Author Response

Responses to reviewer’s comments on the paper entitled

“Numerical simulation of the thermo-mechanical behavior of 6061 aluminum alloy during friction-stir welding” (Ms. ID: JMMP-1773279)

 

The authors would like to express their gratitude to Reviewer for his/her remarks. Below, we provided specific replies to the issues raised.  

 

Note: Reviewer’s comments are highlighted with red. The changes made in the manuscript according to Reviewers’ comments are highlighted with yellow.

 

INTEREST:

The authors present an interesting study about the simulation of the thermomechanical behavior of 6061 aluminum alloy during the Friction Stir Welding (FSW) process, by means of a finite-element model. The paper is well written and organized. Also, the results are interesting and present some advances and good scientific contributions. In addition, the work provides information of interest to the readers of the “Journal of Manufacturing and Materials Processing” (and also to the materials and welding communities), so I recommend the paper for publication after minor revisions.

 

COMMENTS:

Some points for the authors to consider:

1. Please remove "…The introduction should briefly place the study in a broad context and highlight why it is important. It should define the purpose of the work and its significance. The current state of the research field should be carefully reviewed and key publications cited. Please highlight controversial and diverging hypotheses when necessary. Finally, briefly mention the main aim of the work and highlight the principal conclusions. As far as possible, please keep the introduction comprehensible to scientists outside your particular field of research. References should be numbered in order of appearance and indicated by a numeral or numerals in square brackets—e.g., [1] or [2,3], or [4–6]. See the end of the docu-37 ment for further details on references... " at the beginning of the intro section.

Authors’ response

The cited text has been removed from the revised manuscript. The authors would like to apologize for this mistake.

 

2. In the experimental part of the manuscript, the authors mention that several welding tests were carried out at different combinations of tool rotation and translation rates. So I would like to know if there was any attempt to verify (or validate) the values predicted by the finite-element model. For example, for me, it is not clear whether the authors checked if the width of the deformation in a real FSW joint, in fact, reaches ~20-60 mm, thus significantly exceeding the stir zone size.  As the work deals with simulation, I believe this is an important issue and the authors should comment on the validity of their simulated data.

Authors’ response

In order to check the validity of the elaborated model, the authors compared the measured thermal cycles as well as Z-force with predicted ones. Based on the relatively good agreement revealed from this comparison (please see Fig. 2a and Table 3), we do hope that the model was reliable.

 

On the other hand, considering experimental difficulties in measurement of FSW induced strain, the authors do realize that these predictions were not verified.

In the revised manuscript, all these issues were summarized in Section 3.5. “Model validation” (Lines 241-249):  

3.5. Model validation

In order to examine the validity of the elaborated model, the predicted thermal cycles and Z-forces were compared with measured ones (Fig. 2b, supplementary Fig. S2, and Table 3). The relatively good agreement between the data suggests reliability of the simulation results.

On the other hand, it is important to realize that the experimental measurement of the FSW-induced strains and strain rates is challenging. Accordingly, these predictions were not verified.

 

3. In addition, provide recommendations for future research which could advance the state of the art of FSW welding simulation.

Authors’ response

According to the comment, appropriate recommendations have been provided in the revised manuscript (Conclusions, Lines 347-351):

The simulation of the detailed distribution of thermomechanical conditions within the weld zone opens up new perspectives for exploring material behavior. Coupled with the detailed microstructural mapping (e.g., via sample-scale electron backscatter diffraction), it may provide a useful insight into the processing-microstructure relationship and thus refine our fundamental understanding of microstructural mechanisms.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The article is devoted to the simulation of thermomechanical behavior 6061 aluminum alloy in friction stir welding. The article is framed carelessly, not in accordance with the requirements of the journal. The paper needs a lot of work. Here are some notes that should help authors improve peer-reviewed article:

1. From the introduction, it is not clear what caused the need for this work. In the introduction, it is necessary to describe the problems that prompted the authors to carry out numerical studies. Lines 30-38 were not removed from the template.

2. Line 92 indicates the range of strain rates and does not indicate the units of measurement (4-1000 ^s-1).

3. The purpose of the work is to talk about the microstructure and mechanical properties. In the submitted paper, there are no studies of microstructure and mechanical properties. It is necessary to reformulate the purpose of the work or to cite studies of the microstructure and mechanical properties.

4. In the course of research, you studied the welding temperature and the degree of deformation. What did the research results show, how can they be used? What recommendations do you give based on the results of the research?

5. In the  paper, links are given to drawings from the supplementary presentation. How will the readers of the article use this data? I think that the presented figures from the additional presentation should be processed (build graphs on these simulation results), analyzed and added to the main article. The size of the article allows this to be done. You submitted it with 1.5 line spacing, and this publisher's journals are published with 1.0 line spacing.

 

In the presented version, I do not consider it possible to recommend the article for publication. It needs significant improvement.

Author Response

Responses to reviewer’s comments on the paper entitled

“Numerical simulation of the thermo-mechanical behavior of 6061 aluminum alloy during friction-stir welding” (Ms. ID: JMMP-1773279)

 

The authors would like to express their gratitude to Reviewer for his/her remarks. Below, we provided specific replies to the issues raised.  

 

The article is devoted to the simulation of thermomechanical behavior 6061 aluminum alloy in friction stir welding. The article is framed carelessly, not in accordance with the requirements of the journal. The paper needs a lot of work. Here are some notes that should help authors improve peer-reviewed article:

1. From the introduction, it is not clear what caused the need for this work. In the introduction, it is necessary to describe the problems that prompted the authors to carry out numerical studies. Lines 30-38 were not removed from the template.
2. The purpose of the work is to talk about the microstructure and mechanical properties. In the submitted paper, there are no studies of microstructure and mechanical properties. It is necessary to reformulate the purpose of the work or to cite studies of the microstructure and mechanical properties.

Authors’ response

According to the comment, the remaining part of the template (Lines 30-38) have been removed from the revised manuscript. The authors do apologize for this mistake.

Moreover, the introduction section has been deeply revised in order to emphasize the purpose of the present work. In the revised manuscript, this issue has been discussed in Section 1.5 (Lines 103-110). 

The work shown in this paper is a part of a wide-ranging research project aiming to investigate of the effect of FSW on the microstructure and mechanical properties of 6061 aluminum alloy. In the previous works [40-42], the detailed examinations showed an inhomogeneous microstructure distribution in the stir zone. Moreover, it was found that such microstructural gradients may promote abnormal grain growth during the post-weld heat treatment of FSW joints [41, 42]. To elucidate the origin of such a microstructure, it is necessary to know the local variation of thermomechanical conditions within the stir zone. To this end, an appropriate numerical model was elaborated in the present study.

 

2. Line 92 indicates the range of strain rates and does not indicate the units of measurement (4-1000 ^s-1).

Authors’ response

The text of the revised manuscript has been revised according to the comment (Lines 80-81):

…Specifically, the reported peak magnitude of true strain ranged from 5 to 190 [20, 23, 24, 32-34], whereas that of the strain rate was from 4 to 1,000 s^-1[4, 8, 21, 24, 34]…

 

4. In the course of research, you studied the welding temperature and the degree of deformation. What did the research results show, how can they be used? What recommendations do you give based on the results of the research?

Authors’ response

This work is a part of a wide-ranging research project, which aims to investigate the effect of FSW on the microstructure and mechanical properties of 6061 aluminum alloy. From the detailed microstructural examinations in our previous studies, we found that microstructure distribution within the stir zone was not uniform. Moreover, we have established that such microstructural heterogeneities may promote the abnormal grain growth during the post-weld heat treatment of FSW joints. To elucidate the origin of such a microstructure, it is necessary to know the local variation of thermomechanical conditions within the stir zone. To this end, an appropriate numerical model was elaborated in the present study.

In the revised manuscript, these issues have been clarified in Sections 1.5 and 5.

 

Section 1.5 (Lines 103-110):

The work shown in this paper is a part of a wide-ranging research project aiming to investigate of the effect of FSW on the microstructure and mechanical properties of 6061 aluminum alloy. In the previous works [40-42], the detailed examinations showed an inhomogeneous microstructure distribution in the stir zone. Moreover, it was found that such microstructural gradients may promote abnormal grain growth during the post-weld heat treatment of FSW joints [41, 42]. To elucidate the origin of such a microstructure, it is necessary to know the local variation of thermomechanical conditions within the stir zone. To this end, an appropriate numerical model was elaborated in the present study.

 

Section 5 (Lines 347-351):

5) The simulation of the detailed distribution of thermomechanical conditions within the weld zone opens up new perspectives for exploring material behavior. Coupled with the detailed microstructural mapping (e.g., via sample-scale electron backscatter diffraction), it may provide a useful insight into the processing-microstructure relationship and thus refine our fundamental understanding of microstructural mechanisms

 

5. In the paper, links are given to drawings from the supplementary presentation. How will the readers of the article use this data? I think that the presented figures from the additional presentation should be processed (build graphs on these simulation results), analyzed and added to the main article. The size of the article allows this to be done. You submitted it with 1.5 line spacing, and this publisher's journals are published with 1.0 line spacing.

Authors’ response

The authors would like to apologize for this situation. According to the comment, the supplementary materials have been upload to the Internet and appropriate link has been indicated in the revised manuscript (Lines 354-355):

Supplementary Materials: The following supporting information can be downloaded at: https://drive.google.com/file/d/1H1_i99DNoCXQf0WkQRwCouyh5UPHcuos/view?usp=sharin.

 

Moreover, we also adjusted the line spacing in the revised manuscript with journal requirements.

 

In the presented version, I do not consider it possible to recommend the article for publication. It needs significant improvement.

Authors’ response

The authors would like to acknowledge Reviewer for detailed analysis of their work and providing useful recommendations. We do hope that the revised manuscript is suitable for publication.

 

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript for the most part is characterized by terminological and language correctness and proper editorial level. The presented results are well documented, have a logical layout and comprehensive information in the area of the subject matter. The research area and research results presented in the paper contain information of big cognitive value. The conclusions drawn are coherent, logical and aptly describing the observed phenomena.

There are some issues in the manuscript that needs to be addressed, before a possible publication in this journal:

-    First nine lines of the part:
“1. Introduction
1.1. Broad aspects of numerical simulation of friction-stir welding”
are incomprehensible. They should be removed from the manuscript
-    The actual applications of the alloy with respect to the present study may be added.
-    Justify the undertaking of this research work by stating the purpose of the study.
-    Prove a stronger statement of the novelty of this work under introduction section.
-     Provide the experimental setup with its details. The method of fixing the specimen during FSW process is not shown
-    Application only three thermocouples for the measurement should be justified. The temperature values during FSW joining along the entire length of the sample change. Does the comprehensive heat source model and numerical simulation take this into account? A discussion is necessary.
- The manuscript should include the results of a joint's structure investigation

Author Response

Responses to reviewer’s comments on the paper entitled

“Numerical simulation of the thermo-mechanical behavior of 6061 aluminum alloy during friction-stir welding” (Ms. ID: JMMP-1773279)

 

The authors would like to express their gratitude to Reviewer for his/her remarks. Below, we provided specific replies to the issues raised.  

 

The manuscript for the most part is characterized by terminological and language correctness and proper editorial level. The presented results are well documented, have a logical layout and comprehensive information in the area of the subject matter. The research area and research results presented in the paper contain information of big cognitive value. The conclusions drawn are coherent, logical and aptly describing the observed phenomena.

There are some issues in the manuscript that needs to be addressed, before a possible publication in this journal:

(1) First nine lines of the part:
“1. Introduction
1.1. Broad aspects of numerical simulation of friction-stir welding”
are incomprehensible. They should be removed from the manuscript
Authors’ response

The manuscript has been revised according to the comment. The authors would like to apologize for this mistake.

 

(2) The actual applications of the alloy with respect to the present study may be added.

Authors’ response

Appropriate remark has been added to the revised manuscript (Lines 115-117)

The material used in the present investigation was a commercial 6061 aluminum alloy. This alloy is widely used in transportation industry and whose commercial application would benefit from FSW…

(3) Justify the undertaking of this research work by stating the purpose of the study.
Authors’ response

According to the comment, the purpose of this study has been clarified in the revised manuscript (Section 1.5, Lines 103-110):

The work shown in this paper is a part of a wide-ranging research project aiming to investigate of the effect of FSW on the microstructure and mechanical properties of 6061 aluminum alloy. In the previous works [40-42], the detailed examinations showed an inhomogeneous microstructure distribution in the stir zone. Moreover, it was found that such microstructural gradients may promote abnormal grain growth during the post-weld heat treatment of FSW joints [41, 42]. To elucidate the origin of such a microstructure, it is necessary to know the local variation of thermomechanical conditions within the stir zone. To this end, an appropriate numerical model was elaborated in the present study…

 

(4) Prove a stronger statement of the novelty of this work under introduction section.

Authors’ response

According to the comment, the novelty of this work has been emphasized in the revised manuscript (Section 1.5, Lines 111-113):

Moreover, this work represents one of the first models that accounts for the secondary-deformation effect in FSW and systematically examines the influence of FSW variables on the peak welding temperature and the FSW-induced strain.

(5) Provide the experimental setup with its details. The method of fixing the specimen during FSW process is not shown

Authors’ response

According to the comment, the clamping fixture for FSW machine has been shown in supplementary Figure S1b

(6) Application only three thermocouples for the measurement should be justified. The temperature values during FSW joining along the entire length of the sample change. Does the comprehensive heat source model and numerical simulation take this into account? A discussion is necessary.

Authors’ response

Appropriate discussion has been added to the revised manuscript according to the comment (Lines 137-139):

It is important to emphasize that Z-force was found to be nearly unchanged during the stable stage of FSW. From this observation, it was suggested that the FSW temperature was also nearly constant along the weld path.

(7) The manuscript should include the results of a joint's structure investigation

Authors’ response

According to the comment, microstructural characterization of FSW joints has been added to the revised manuscript as supplementary data. These can be viewed/downloaded using the link:

https://drive.google.com/file/d/11hESJgLf4bi8sSaIW5FEHeZxL3sHhZYS/view?usp=sharing

 

Appropriate remarks have been added to the revised manuscript

 

Page 3, footnote:

Microstructural characterization of the studied welds is shown in supplementary data “Microstructure”.  

 

Lines 356-358:

Supplimentary microstructural data:

https://drive.google.com/file/d/11hESJgLf4bi8sSaIW5FEHeZxL3sHhZYS/view?usp=sharing

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors have corrected the article according to my comments. I recommend the article for publication.