Quantifying the Effects of Grain Refiners Al-Ti-B and La on the Microstructure and Mechanical Properties of W319 Alloy

Round 1

Reviewer 1 Report

The abstract requires rewriting. It's not well balanced, as too much information about the justification is provided whereas there is a lack of information about methodology. The abstract should be a summary of the article (with a similar structure).

There is an abundant use of technology in the characterization of these grain refined Al alloys. Yet, such technology becomes irrelevant when not sufficient statistical analysis is used, reported, and evaluated. One always needs to know information about the variability of the results. This is lacking in the manuscript except in the assessment of the mechanical properties, which led me to a different conclusion (last claim by the authors).

The manuscript is high quality in an overall analysis. Some of my concerns or comments are included in the attached document.

Comments for author File: Comments.pdf

Author Response

1. The abstract requires rewriting. It's not well balanced, as too much information about the justification is provided whereas there is a lack of information about methodology. The abstract should be a summary of the article (with a similar structure).

Response: Thank you very much for your comments. After careful consideration, the revisions are as follows“It is well-known that the microstructure distribution in recycled Al-Si alloys have a large impact on the final mechanical properties. In this study, the microstructure including Fe-rich intermetallics and microporosity were quantitatively characterized by using multi-scale characterization (OM,SEM/EDS, XCT) with microalloying rare earth(RE) elements and traditional grain refiners as the objects of study. It was found that the addition of Al-Ti-B to W319 recycled aluminum alloy reduces the grain size and Fe-rich intermetallic compounds, while the addition of La facilitates the transformation of harmful β-Fe into less harmful particles and the densification of coarse eutectic Si, promoting the refining effects on the grains additionally. Therefore, the RE and Al-Ti-B master alloy can be a potential new grain refining agents, especially for Al-cast alloys when the ductility is critical for designing. The improvement in elongation far exceeds the original level, up to 69.60%, while maintaining the same level of strength or even better; while the excessive addition of La may lead to the depletion of Cu and Ti elements during heat-treatment, degrading ductility and strength.”

2. There is an abundant use of technology in the characterization of these grain refined Al alloys. Yet, such technology becomes irrelevant when not sufficient statistical analysis is used, reported, and evaluated. One always needs to know information about the variability of the results. This is lacking in the manuscript except in the assessment of the mechanical properties, which led me to a different conclusion (last claim by the authors).

Response: Thank you very much for your comments. The manuscript has been revised accordingly.

3. The manuscript is high quality in an overall analysis. Some of my concerns or comments are included in the attached document.

Response: Thanks again for your guidance. We have revised them carefully.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors presented the results of the effect of grain refiners of La and Al-Ti-B on the microstructure and mechanical properties of W319 alloy. Work needs improvement according to comments.

Comment 1. Introduction -The sentences are long and too complex!. Page 2, line 68-75, the purpose of the work is not evident! Use the passive voice!

Comment 2. The formatting of Table 1, page 3 and Table 2, page 7 should be corrected.

Comment 3. Correct the size of the description font on the coordinate axes.

Comment 4. Page 5, line 163, line 170 and line 182-use the correct sequence of equations!

Comment 5. Chapter 4 should be further elaborated on with the results obtained from the research (not only refer to figures 4 and 8)!

Author Response

The authors presented the results of the effect of grain refiners of La and Al-Ti-B on the microstructure and mechanical properties of W319 alloy. Work needs improvement according to comments.

Comment 1. Introduction -The sentences are long and too complex!. Page 2, line 68-75, the purpose of the work is not evident! Use the passive voice!

Response: Thank you for your comments. We have made changes according to your suggestions.

Comment 2. The formatting of Table 1, page 3 and Table 2, page 7 should be corrected.

Response: Thank you for your comments. This has been corrected.

Comment 3. Correct the size of the description font on the coordinate axes.

Response: Yes, we have made those corrections.

Comment 4. Page 5, line 163, line 170 and line 182-use the correct sequence of equations!

Response: Yes, we have made the changes.

Comment 5. Chapter 4 should be further elaborated on with the results obtained from the research (not only refer to figures 4 and 8)!

Response: Yes, this part of the discussion was not sufficient. Thank you for pointing it out. We have made those changes.

Author Response File: Author Response.pdf

Reviewer 3 Report

Drafted paper “ Quantifying the effects of grain refiners of La and Al-Ti-B on 2 the microstructure and mechanical properties of W319 alloy” contain a large investigation of structure and properties.  Some major points should be improved.

1. The topic of the manuscript aimed on the grain refining. The grain structure was not investigated in the paper. The effect of additives was applied on dendritic cell structure. But Ti is the best grain refiner.

Manuscript constructed with contradictions.

2. The abbreviations should be introduced before used.
3. Measured values. Are the 2 decimal statistically significant? Please round the measured values in accordance with standard deviation.
4. La is one of the perspectives REM for improving the structure and properties of the Al alloys. Please provide the comparison, for example, with effect of Er, Y, Yb in A-Si alloys.

Author Response

Drafted paper “ Quantifying the effects of grain refiners of La and Al-Ti-B on 2 the microstructure and mechanical properties of W319 alloy” contain a large investigation of structure and properties.  Some major points should be improved.

1. The topic of the manuscript aimed on the grain refining. The grain structure was not investigated in the paper. The effect of additives was applied on dendritic cell structure. But Ti is the best grain refiner.

Response: Thank you for pointing out this. The topic of this manuscript include the La and TiB₂ effects on the grain refining. The grain structure was characterized by OM and SEM images. The cell structure correlates to the grain structure. It is shown in this study that La is also a good refiner besides Ti.

2. Manuscript constructed with contradictions.

Response: Thank you for your comments. This has been corrected.

3. The abbreviations should be introduced before used.

Response: Thank you for your comments. We have made changes according to your suggestions.

4. Measured values. Are the 2 decimal statistically significant? Please round the measured values in accordance with standard deviation.

Response: Thank you for your comments. We have made rounded the values as suggested.

5. La is one of the perspectives REM for improving the structure and properties of the Al alloys. Please provide the comparison, for example, with effect of Er, Y, Yb in A-Si alloys.

Response: Thank you for your comments. We added comparison as you suggested.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Just one thing: please remove the characterization techniques acronyms in the abstracts. Abstracts should not contain acronyms in general. 

Author Response

Just one thing: please remove the characterization techniques acronyms in the abstracts. Abstracts should not contain acronyms in general. 

Response: Thank you very much for your comments. We have revised it accordingly.

Author Response File: Author Response.pdf

Reviewer 3 Report

The Authors should be more detailed use the terms and its application.

Grain refining and dendritic cell structure refining based on different mechanisms.

 Grain refining based on the heterogeneous nucleation on the primary intermetallics with the same lattice structure.

Dendritic cell structure (number of dendritic axes) depends on cooling rate during solidification first of all.

In this case very important to combine grain structure investigation with dendritic cell structure analysis.

The grain structure did not investigate in the present paper.

Some minor comments:

1. Fig. 1 a. Temperature of the section did not indicated.
2. Fig2b. What is the reason of increasing Al2Cu phase fraction at about 350C?
3. The effect of small Ti addition was investigated, but not a master alloy Al-Ti-B. Because no comments about TiB2 from master alloy are present in the paper.

In the topic should be “effect of trace Ti and La”, for example.

4. Prevue comment 3 - Measured values. Are the 2 decimal statistically significant? Please round the measured values in accordance with standard deviation.

Not corrected.

5. Fig 6a. Hardness is not sensitive to microstructure changes in the present investigation. All alloys have the same HV in accordance the standard deviation.

Figure and discussion are uninformative.

6. The same (see comment 5) for Fig 6b. The YS and UTS is the same for all compositions. But elongation slightly increases. What is the reason for this phenomenon?
7. Comparison properties of as cast and aged alloys is very strange. Of course after aging mechanical properties increased.
8. The negative effect of La on mechanical properties was demonstrated. The negative effect leaves a negative impression from paper.

Please in detailed see the investigations of Colombo, Pozdniakov et.al. The same effect on the room temperature strength was indicated after REM addition in the Al-Si-Cu-Mg alloys, but increasing in high temperature strength was achieved.

Author Response

The Authors should be more detailed use the terms and its application. Grain refining and dendritic cell structure refining based on different mechanisms. Grain refining based on the heterogeneous nucleation on the primary intermetallics with the same lattice structure. Dendritic cell structure (number of dendritic axes) depends on cooling rate during solidification first of all. In this case very important to combine grain structure investigation with dendritic cell structure analysis. The grain structure did not investigate in the present paper. Response: First of all, thank you very much for your valuable comments. We have changed the place where there the descriptions of "Grain refining" and "dendritic cell structure refining" are confusing. In most cases, "microstructure" is used instead. We chose to quantify SDAS rather than grain size for two reasons: 1. the addition of 7.3 wt.% Si makes it difficult to observe grain boundaries, while SDAS statistics are particularly accurate and efficient; 2. there are reports indicating that SDAS is a more dominant factor than GS in influencing the mechanical properties of the alloy. And finally we observed, as expected, the effect of AlTiB and La on SDAS, and obtained the quantitative data. Some minor comments: 1. Fig. 1 a. Temperature of the section did not indicated. Response: Thank you for your comments. We have made the revision. 2. Fig2b. What is the reason of increasing Al2Cu phase fraction at about 350C? Response: At about 350 °C, the generation of La-rich phase (indicated by the yellow line) causes the reduction of Al2Cu as can be seen in Figure 1(b), which has been described in the text. Also the SEM/EDS results below confirm that the reaction of La with Cu produces La-rich phase, which is shown in the phase diagram as the reduction of Al2Cu. 3. The effect of small Ti addition was investigated, but not a master alloy Al-Ti-B. Because no comments about TiB2 from master alloy are present in the paper.In the topic should be “effect of trace Ti and La”, for example. Response: The trace Ti in this paper is added in the form of Al-5Ti-1B. It is well known that Al3Ti and TiB2 in Al-5Ti-1B act as heterogeneous nuclei. TiB2 is very stable and has a melting point close to 3000°C; it does not dissolve or react with La, so our focus is on the "effect of Al-Ti-B and La ". 4. Prevue comment 3 - Measured values. Are the 2 decimal statistically significant? Please round the measured values in accordance with standard deviation.Not corrected. Response: Thank you for your suggestions. All two-digit statistics are rounded except for the necessary decimals (mainly concentrated in the eutectic Si chapter). 5. Fig 6a. Hardness is not sensitive to microstructure changes in the present investigation. All alloys have the same HV in accordance the standard deviation. Figure and discussion are uninformative. Response: We have added more discussions in this section which is detailed in the discussion. 6. The same (see comment 5) for Fig 6b. The YS and UTS is the same for all compositions. But elongation slightly increases. What is the reason for this phenomenon? Response: Thank you for your comments. We have added the corresponding parts in the discussion. 7. Comparison properties of as cast and aged alloys is very strange. Of course after aging mechanical properties increased. Response: Thank you for your comments. This paper focuses on the effect of grain refiners and La on W319 alloy. In order to get a more complete conclusion, so the characterization experiments and discussions are done for both the as-cast and heat-treated states, and the purpose is not to highlight the property changes brought by the heat treatment process. For this reason, we set up all the experiments for this paper. 8. The negative effect of La on mechanical properties was demonstrated. The negative effect leaves a negative impression from paper. Response: Thank you again for your seriousness in finding the shortcomings of the article. All experiments and data processing were performed according to the specification. Reviewing the entire article, both thermodynamic calculations, microstructure characterization and mechanical property tests show that La can have multiple effects, both positive and negative. The result is that it improve plasticity to some extent in the as-cast state; however, after heat treatment, the negative effects dominate. So we believe such a conclusion is both reliable and practical. Please in detailed see the investigations of Colombo, Pozdniakov et.al. The same effect on the room temperature strength was indicated after REM addition in the Al-Si-Cu-Mg alloys, but increasing in high temperature strength was achieved. Response: We are sorry but we did not find the literature from Colombo, Pozdniakov et.al. on rare earth metal additions. The following literatures have been found which differs in some extent from what was studied in our paper： [1] Barkov RY, Mochugovskiy AG, Khomutov MG, Pozdniakov AV. Effect of Zr and Er Small Additives on the Phase Composition and Mechanical Properties of Al–5Si–1.3Cu–0.5Mg Alloy. The Physics of Metals and Metallography. 2021. [2] Colombo M, Gariboldi E, Morri A. Er addition to Al-Si-Mg-based casting alloy: Effects on microstructure, room and high temperature mechanical properties. Journal of Alloys and Compounds. 2017; 708:1234-44. [3] Pozdniakov AV, Barkov RY, Amer SM, Levchenko VS, Kotov AD, Mikhaylovskaya AV. Microstructure, mechanical properties and superplasticity of the Al–Cu–Y–Zr alloy. Materials Science and Engineering: A. 2019; 758:28-35.

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

Authors try to improve paper in accordance of the Reviewer comments. Unfortunately some of them were ignore. Please improve the manuscript in the following points.

1. Difficult does it mean impossible. The oxidation electrochemical process is very simple to see the grain structure and it is not depend on Si content in the alloy.
2. Which report indicate that SDAS is dominant factor? To demonstrate it is necessary to see the grain structure. The simple dependencies of YS on SDAS and grain structure are existing. Please provide an evidence.
3. The publication which are necessary to the present paper.

Mater. Sci. Eng. A 2018. V.713 P. 151-160.

Materials Letters Volume 271, 15 July 2020, 127795

Journal of Alloys and Compounds 806 (2019) 909-916.

1. Alloys Compd. 487 (1e2) (13 November 2009) 157-162
2. Mater. Eng. Perform. 25 (7) (July 2016) 2799-2813

Physics of Metals and Metallography, 2021, 122(6) 614–620

Physics of Metals and Metallography, 2021, 122(2)161–168

METALLURGICAL AND MATERIALS TRANSACTIONS A  44, 669–681 (2013)

Rare Metals volume 36, pages95–100 (2017)

Author Response

Comments and Suggestions for Authors

Authors try to improve paper in accordance of the Reviewer comments. Unfortunately some of them were ignore. Please improve the manuscript in the following points.

1. Difficult does it mean impossible. The oxidation electrochemical process is very simple to see the grain structure and it is not depend on Si content in the alloy.

Response: Thank you again for pointing out the shortcomings of our work. We completely agreed with the reviewer that after the oxidation electrochemical process, normally the grain structure can be seen and statistics can be generated. Indeed, we have tried several methods: 1. we etched the sample with aqua regia (HCl: HNO3 = 3:1) solution for 30 seconds according to Ref. [1]; 2. we etched the sample with 60 vol% HCl, 30 vol% HNO3, 5 vol% HF and 5 vol% H₂O for 60 seconds at room temperature according to Ref. [2]. Neither of them give us the satisfactory images as shown in the following figures. This is because the addition of RE elements and Fe rich intermetallics really change the corrosion resistance locally, producing biased view of grain boundaries. Therefore, the quantification of grain size from those images will inevitably bring statistic errors. We rely on the SDAS from the unetched samples instead where there was no localized corrosion of Fe or RE elements.

•                                  (b)

Fig. 01 the optical micrograph of dendritic structures of Al-Si-Cu alloys with Fe and RE additions showing the localized corrosion of Fe-rich intermetallics and RE elements

• Liu W, Xiao W, Xu C, Liu M, Ma C. Synergistic effects of Gd and Zr on grain refinement and eutectic Si modification of Al-Si cast alloy. Materials Science and Engineering: A. 2017; 693:93-100.
• Xu C, Xiao W, Hanada S, Yamagata H, Ma C. The effect of scandium addition on microstructure and mechanical properties of Al–Si–Mg alloy: A multi-refinement modifier. Materials Characterization. 2015; 110:160-9.

1. Which report indicate that SDAS is dominant factor? To demonstrate it is necessary to see the grain structure. The simple dependencies of YS on SDAS and grain structure are existing. Please provide an evidence.

Response: In the previous publications, the SDAS quantification has been directly linked to mechanical properties. In the following reports, the authors have claimed the more appropriate indicator of mechanical properties by SDAS:

• Ghassemali E, Riestra M, Bogdanoff T, Kumar BS, Seifeddine S. Hall-Petch equation in a hypoeutectic Al-Si cast alloy: grain size vs. secondary dendrite arm spacing. Procedia Engineering. 2017; 207:19-24.
• Yan K, Huang W, Zuo Z. Microstructure based analysis and predictive modeling of cast Al7Si1.5Cu0.4Mg alloy mechanical properties. Materials Today Communications. 2022; 30:2352-4928.

1. The publication which are necessary to the present paper.

Response: We thank the reviewer for providing us the list of references. All the articles are very valuable to us. In fact, we have cited some of them in our last revision. As the reviewer suggested, we have add more citations of those useful articles.

Mater. Sci. Eng. A 2018. V.713 P. 151-160.

Materials Letters Volume 271, 15 July 2020, 127795

Journal of Alloys and Compounds 806 (2019) 909-916.

Alloys Compd. 487 (1e2) (13 November 2009) 157-162

Mater. Eng. Perform. 25 (7) (July 2016) 2799-2813

Physics of Metals and Metallography, 2021, 122(6) 614–620

Physics of Metals and Metallography, 2021, 122(2)161–168

METALLURGICAL AND MATERIALS TRANSACTIONS A  44, 669–681 (2013)

Rare Metals volume 36, pages95–100 (2017)

Author Response File: Author Response.pdf