Microstructure Evolution and Mechanical Property Response of 3D-Printed Scalmalloy with Different Heat-Treatment Times at 325 °C

Round 1

Reviewer 1 Report

The topic and the paper are interesting. Heat treatments after 3d printing is an important topic of research. Although the heat treatment conditions could be increased to cover different temperatures, the present results shed some light on the occurrence of precipitation in this aluminum alloy. One major correction and a few minor corrections are needed before acceptance. 

Major correction: the mechanical properties were evaluated using tensile test without extensometer. Therefore the authors must remove any information regarding Young modulus on section 3.2. Note that nanoindentation is not descrived in experimental procedure and not a reliable test to determine young modulus variations. Also, the samples subjected to heat treatments at 4, 24 and 48 hours do not display any significant difference in tensile test. The variations in stress in the yield region are within the errror of the test. All heat treated samples show similar stress strain curves.

 

Minor corrections:

The authors should clarify the composition of the alloy in the abstract and introduction as it is not only Al-Sc alloy.

The TEM images show a very limited area of the material. Please clarify how many TEM images and observed area were used to estimate Al3Sc precipitate size. 

The authors attribute the lack of recrystallization to the Al3Sc precipitates. Recrystallization requires a previous cold deformation in order to provide driving force. 3d printed samples do not undergo cold deformation and therefore it is expected that recrystallization will be difficult.

The authors could rewrite some sentences with improved language. 

Author Response

Response to Review

 

Manuscript ID: metals-1151975  

Title: Microstructure Evolution and Mechanical Property Response of 3D Printed Scalmalloy with Different Heat-Treatment Times at 325 ^oC

Journal: Metals

Authors: C.N. Kuo*, P.C. Peng, D.H. Liu, and C.Y. Chao

 

Mar. 19, 2021

 

Dear editor and reviewer:

 

Thank you very much for the review. The reviewer’s constructive comments can greatly strengthen our paper and have provided many useful suggestions. We have tried our best in replying or adding new information in text. The point to point responses are described below.

 

Reviewer #1:

• The topic and the paper are interesting. Heat treatments after 3d printing is an important topic of research. Although the heat treatment conditions could be increased to cover different temperatures, the present results shed some light on the occurrence of precipitation in this aluminum alloy. One major correction and a few minor corrections are needed before acceptance. 

Reply: Thanks for the valuable comments. We have tried our best in revising the manuscript.

• Major correction:

1. the mechanical properties were evaluated using tensile test without extensometer. Therefore the authors must remove any information regarding Young modulus on section 3.2. Note that nanoindentation is not described in experimental procedure and not a reliable test to determine young modulus variations. Also, the samples subjected to heat treatments at 4, 24 and 48 hours do not display any significant difference in tensile test. The variations in stress in the yield region are within the error of the test. All heat-treated samples show similar stress strain curves.

Reply: Thank you very much for the valuable suggestions. After thorough deliberation, the nanoindentation is not a reliable test to determine young modulus variations, especially for such materials. Therefore, we have removed the information regarding Young’s modulus and modified the manuscript and Table 4.

    Regarding the yield stress, the yield stress results of each group of samples were calculated by averaging three data. The yield stress of each sample was obtained from the intersection of the ss curve and the parallel line with 0.2% offset. Although the Young’s modulus and the strain at failure results were similar for all samples, the yield stress results for each group of samples showed a difference. We have modified Fig. 8 to clarify the difference in yield stress.

 

Fig. 8. (b) the enlarged image shows the difference in yield stress of heat-treated samples.

 

• Minor corrections:

1. The authors should clarify the composition of the alloy in the abstract and introduction as it is not only Al-Sc alloy.

Reply: Thank you for the comment. We have modified the manuscript and added the composition of the alloy (Al-4.49Mg-0.71Sc-0.51Mn-0.27Zr-0.07Fe-0.03Si) in the abstract and introduction.

 

2. The TEM images show a very limited area of the material. Please clarify how many TEM images and observed area were used to estimate Al3Sc precipitate size. 

Reply: Thank you for the comment. The Al3Sc precipitate size was estimated by three TEM images for each group of samples which the observed area was about 1400 nm * 970 nm and the foil thickness was 100 nm. We have also modified the experimental procedure.

 

3. The authors attribute the lack of recrystallization to the Al3Sc precipitates. Recrystallization requires a previous cold deformation in order to provide driving force. 3d printed samples do not undergo cold deformation and therefore it is expected that recrystallization will be difficult.

Reply: Thank you, we have modified the manuscript based on your valuable suggestion in page 5.

 

4. The authors could rewrite some sentences with improved language. 

Reply: Thank you for the suggestion. We have modified the manuscript again, hope it is better now.

 

If there is anything that we should do further, please do not hesitate to inform us. Thanks.

 

Che-Nan Kuo, Assistant Professor

Asia University, Taichung, Taiwan

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper “Microstructure Evolution and Mechanical Property Response of 3D Printed Scalmalloy with Different Heat-Treatment Times at 325 °C” is devoted to the investigation of the structure and mechanical properties of the Al-Mg-Sc alloy for additive manufacturing. The topic of the paper is actually due to the high potential application of selective laser melting for obtaining a supersaturated solid solution. The paper is well written and maybe published after correction accordingly following comments:

1. Why the authors choose one stage heat treatment at the temperature of 325 °C? It is known that optimal mechanical properties in Al-Mg-Sc-Zr alloys are achieved during two-stage heat treatment [10.1016/j.matchar.2018.02.030, 10.1088/2053-1591/ab5bea].
2. How was measured the volume fraction of the precipitates? The thickness of the foils which were used for TEM is needed for the correct calculation of the volume fraction. What value of the foil’s thickness was used by the authors? As we can see in Figure 5 there is a significant difference in the amount of the precipitates in the as-built state and after heat treatment. However, the values of the volume fraction differ less than twice in Table 3.
3. The values of Young’s modulus for the alloys after heat treatment seem to be incorrect and should be removed from the paper.
4. It is better to use Orowan’s law for the calculation of the yield strength instead of the dependence on volume fraction/size ratio.
5. Minor corrections are also required:

• The name of the alloy (Al-0.7Sc) is not correct in the Abstract. The magnesium and zirconium are also important alloying elements and should be in the description of the alloy.
• The number of digits in the values in Tables 2, 3, 4 should be decreased accordingly the value of experimental error.

Author Response

Response to Review

Manuscript ID: metals-1151975  

Title: Microstructure Evolution and Mechanical Property Response of 3D Printed Scalmalloy with Different Heat-Treatment Times at 325 ^oC

Journal: Metals

Authors: C.N. Kuo*, P.C. Peng, D.H. Liu, and C.Y. Chao

 

Mar. 19, 2021

 

Dear editor and reviewer:

Thank you very much for the review. The reviewer’s constructive comments can greatly strengthen our paper and have provided many useful suggestions. We have tried our best in replying or adding new information in text. The point to point responses are described in the PDF file.

 

If there is anything that we should do further, please do not hesitate to inform us. Thanks.

Che-Nan Kuo, Assistant Professor

Asia University, Taichung, Taiwan

Author Response File: Author Response.pdf

Reviewer 3 Report

Dear authors, the article is quite interesting. In my opinion it is generally a good but short work. While I do not have any major substantive comments, its reading leaves me unsatisfied. I would add SEM pictures of the tested powder, I would wrote the chemical composition in the table. If the tests for densities after heat treatment were performed, they should be included, if not, then write why not. Figures 2, 3 and 7 should be enlarged. The quality of figure 4 is poor. I would correct the conclusions because they are too general.

Author Response

Response to Review

Manuscript ID: metals-1151975  

Title: Microstructure Evolution and Mechanical Property Response of 3D Printed Scalmalloy with Different Heat-Treatment Times at 325 ^oC

Journal: Metals

Authors: C.N. Kuo*, P.C. Peng, D.H. Liu, and C.Y. Chao

Mar. 19, 2021

 

Dear editor and reviewer:

Thank you very much for the review. The reviewer’s constructive comments can greatly strengthen our paper and have provided many useful suggestions. We have tried our best in replying or adding new information in text. The point to point responses are described below.

 

Reviewer #3:

• Dear authors, the article is quite interesting. In my opinion it is generally a good but short work. While I do not have any major substantive comments, its reading leaves me unsatisfied. I would add SEM pictures of the tested powder, I would wrote the chemical composition in the table. If the tests for densities after heat treatment were performed, they should be included, if not, then write why not. Figures 2, 3 and 7 should be enlarged. The quality of figure 4 is poor. I would correct the conclusions because they are too general.

Reply: Thanks for the valuable comments. We have tried our best in revising the manuscript.

1. We have added the SEM pictures of the tested powder, as shown in Fig. 1.
2. The table of the chemical composition was suggested to be withdrawn since it already presented in the paper we published before (C. N. Kuo*, C. K. Chua, P. C. Peng, Y. W. Chen, S. L. Sing, S. Huang, and Y. L. Su, “Microstructure evolution and mechanical property response via 3D printing parameter development of Al–Sc alloy”, Virtual and Physical Prototyping, 15 (1) (2020) 120-129.).
3. The density tests were performed samples on all samples, and the measured density is 666±0.006 g/cm³ for all samples with/without heat-treatment.
4. We have enlarged the figures.
5. We have modified Fig. 4.
6. We have modified the conclusion, hope it is better now.

 

If there is anything that we should do further, please do not hesitate to inform us. Thanks.

 

Che-Nan Kuo, Assistant Professor

Asia University, Taichung, Taiwan

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors have answered previous comments and improved the manuscript. The paper may be accepted for the publication in present state.