Pressure-Less Liquid-Phase Sintering of Aluminum-Based Materials

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Author wrote about the  the densification of Al and Al-based materials via pressure-less liquid phase sintering. However, the following points need to be clarified.

1. The Al and AlSi12 powders were blended and homogenized for 5 min at 1200 rpm using a planetary mixer. It can be expected that during the mixing process, the interaction of the initial components occurs, which leads to the formation of large agglomerates. This point is not discussed in the article.

2. The scale is not specified in Figure 3.

3. The eutectic alloy AlSi12 has a melting point of 577 degrees Celsius, while the individual metals Al and Si melt at 660 degrees Celsius and 1414 degrees Celsius. All sintering temperatures used are below the melting point of aluminum. Why are these temperatures selected?

4. What is the mechanism of hardening of aluminum alloy introduction of AlSi12? It is necessary to compare the properties of the obtained alloys with the data of other researchers (for example - Kekana, N., Shongwe, M.B., Mpofu, K. et al. A review on factors influencing mechanical properties of AlSi12 alloy processed by selective laser melting. Int J Adv Manuf Technol 121, 4313–4323 (2022). https://doi.org/10.1007/s00170-022-09582-6  etc.).

 

 

Author Response

In this work, the authors explored the densification of Al and Al-based materials via pressure-less liquid phase sintering. Samples containing 4-20 vol.% AlSi12 sintered at 640 °C for 1 h obtained the highest relative density (RD) and lowest global porosity (GP) without any shape deformation. An expanded lattice parameter with minimal microstrain and crystallite size closely matching those of the initial Al powder was found. The samples with a relative density greater than 90% exhibited thermal conductivities ranging from 170 to 200 W/mK, with an average hardness of 29 HV5. The Al-based material compacted at 200 MPa and with 15 vol.% AlSi12 achieved the highest RD of approximately 99 % with a thermal conductivity of 195 W/mK at 30 °C and 190 W/mK at 70 °C, along with a hardness of 30 HV5. However, there are still some issues which need to be clarified:

1. The abstract is not well written. Pls revise it.

The abstract has been revised

2. There are plenty of grammar errors or typos, such as in line 81 and 83,”AlSi12”; between line 95 and 96, the font size is too big (is it possible to write a paragraph instead of using a table?); line 123, page 3, “This outcome is logical,”; between 168 and 169, page 5, I do not understand the sentence “This is consistent with...”; line 172, page 5, “maybe attributed” ... As for the rest of the manuscript, there are still some grammar errors.

The grammatical errors have been corrected and the table was replaced by a paragraph. This helps the understanding of the process. Moreover, the grammar has been checked twice by a native English speaker (Pr. Yongfeng Lu, Lott Distinguished Professor of Electrical and Computer Engineering, Mechanical and Materials Engineering SPIE, LIA, OSA, and IAPLE Fellow)

 

3. What is total amount of Al and AlSi12? Different amount means the different difficulty for processing.

Each mix is done for a certain mass. Indeed, for example, for a batch of 5 grams we weight the amount of Al and the amount of AlSi12 necessary regarding the needed volume percentage of AlSi12.

4. There is some amount of Al evaporating when the temperature increases to above 600 C. Did the authors consider this error?

Yes, some amount of Al can be evaporated during the sintering cycle. However, we did not consider this error because there was no Al on the surface of the tube after the sintering step.

5. The hardness increase of Al and AlSi12 may be due to the oxidation of Al, instead of the addition of AlSi12. The authors should trace the content of oxygen in the materials.

The oxidation of the samples cannot be different regarding the fact that all the compared samples were sintered in the same furnace during the same cycle under controlled atmosphere.

6. Why it is so necessary to densify Al.

Aluminum needs to be the more densified as possible to be used in the different applications of Aluminum. Moreover, densify Aluminum by free sintering could be a solution to reduce the costs to produce Al based composites usually fabricated using either SPS or uniaxial hot pressing.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Review

In this work, the authors explored the densification of Al and Al-based materials via pressure-less liquid phase sintering. Samples containing 4-20 vol.% AlSi12 sintered at 640 °C for 1 h obtained the highest relative density (RD) and lowest global porosity (GP) without any shape deformation. An expanded lattice parameter with minimal microstrain and crystallite size closely matching those of the initial Al powder was found. The samples with a relative density greater than 90% exhibited thermal conductivities ranging from 170 to 200 W/mK, with an average hardness of 29 HV5. The Al-based material compacted at 200 MPa and with 15 vol.% AlSi12 achieved the highest RD of approximately 99 % with a thermal conductivity of 195 W/mK at 30 °C and 190 W/mK at 70 °C, along with a hardness of 30 HV5. However, there are still some issues which need to be clarified:

1. The abstract is not well written. Pls revise it.

2. There are plenty of grammar errors or typos, such as in line 81 and 83,”AlSi12”; between line 95 and 96, the font size is too big (is it possible to write a paragraph instead of using a table?); line 123, page 3, “This outcome is logical,”; between 168 and 169, page 5, I do not understand the sentence “This is consistent with...”; line 172, page 5, “maybe attributed” ... As for the rest of the manuscript, there are still some grammar errors.

3. What is total amount of Al and AlSi12? Different amount means the different difficulty for processing.

4. There is some amount of Al evaporating when the temperature increases to above 600 C. Did  the authors consider this error?

5. The hardness increase of Al and AlSi12 may be due to the oxidation of Al, instread of the addition of AlSi12. The authors should trace the content of oxygen in the materials.

6. Why it is so necessary to densify Al.

 

Comments on the Quality of English Language

English language need to be improved.

Author Response

Author wrote about the densification of Al and Al-based materials via pressure-less liquid phase sintering. However, the following points need to be clarified.

1. The Al and AlSi12 powders were blended and homogenized for 5 min at 1200 rpm using a planetary mixer. It can be expected that during the mixing process, the interaction of the initial components occurs, which leads to the formation of large agglomerates. This point is not discussed in the article.

Yes, interactions between Al and AlSi12 can occurs. However, in our case, no evidences of agglomerates or interactions have been found. That is why there is no discussion about that point in the article

2. The scale is not specified in Figure 3.

The scale has been added in the Figure 3.

3. The eutectic alloy AlSi12 has a melting point of 577 degrees Celsius, while the individual metals Al and Si melt at 660 degrees Celsius and 1414 degrees Celsius. All sintering temperatures used are below the melting point of aluminum. Why are these temperatures selected?

These temperatures were selected to guarantee the melting of the AlSi12 phase and to be sure that the Al is not melting. Indeed, liquid phase sintering is mainly a solid process. The aim of that study is to find a way to densify Aluminum objects in a certain shape. If we melt totally the Al the shape will not be maintained.

4. What is the mechanism of hardening of aluminum alloy introduction of AlSi12? It is necessary to compare the properties of the obtained alloys with the data of other researchers (for example - Kekana, N., Shongwe, M.B., Mpofu, K. et al.A review on factors influencing mechanical properties of AlSi12 alloy processed by selective laser melting. Int J Adv Manuf Technol121, 4313–4323 (2022). https://doi.org/10.1007/s00170-022-09582-6  etc.).

Thank you for this remark. It is hard to compare our materials (Al + AlSi12) fabricated by powder metallurgy (with a small volume fraction of AlSi12) with AlSi12 materials usually fabricated by foundry process. Hardening of Al alloys is well known and usually attributed impending dislocation movements (as already written in our paper “Alloying is a common technique employed to strengthen metals by impeding dislocation movements. Its effectiveness is influenced by several factors, such as alloying process, amount of alloying element, and its manner in which it dissolves within the matrix [35-36].” In our material we suggest that this increase of hardness is mainly due to the increase of density that rather than common hardening effect due to alloying element (see the sentence in our paper. “The addition of AlSi₁₂ in the Al-based samples had an overall positive effect on hardness, attributed to the improved material density compared to samples without a sintering aid »).

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

 

I have examined with interest the manuscript. The subject is interesting, and it is one to which the authors may add some contributions, but the paper needs many modifications. The authors should better clarify the novel contribution of the current research.

The title should be changed to better reflect all the experimental work.

Further references from literature are needed, e.g. bellow:

Wu, L., Yu, Z., Liu, C., Ma, Y., Huang, Y., Wang, T., Yang, L., Yan, H. and Liu, W., 2021. Microstructure and tensile properties of aluminum powder metallurgy alloy prepared by a novel low-pressure sintering. Journal of Materials Research and Technology, 14, pp.1419-1429.

Godbole, K., Bhushan, B., Murty, S.N. and Mondal, K., 2024. Al-Si controlled expansion alloys for electronic packaging applications. Progress in Materials Science, p.101268.

*Cuzacq, L., Atchi, I., Bobet, J.L., Lu, Y. and Silvain, J.F., 2024. Pressureless sintering of Al/diamond materials using AlSi12 liquid phase. Materials Letters, p.137788.

The authors should explain why the *Cuzacq, L…. paper wasn’t included in the list of References.

Scale bars should be added to all pertinent Figures - Figure 2 and Figure 3.

The authors should elaborate on accuracy and repeatability of the measurements, when applicable, e.g. relative density and other properties.

The authors should elaborate on the characteristic defects (pores and cracks) found in the material/samples, please include cracks in your discussion; NDT methods to be used for characterizing the discontinuities/defects should be presented and discussed.

 

I hope the above comments help to improve a future version of the paper.

 

Comments on the Quality of English Language

No further comments

Author Response

I have examined with interest the manuscript. The subject is interesting, and it is one to which the authors may add some contributions, but the paper needs many modifications. The authors should better clarify the novel contribution of the current research.

 

1. The title should be changed to better reflect all the experimental work.

Thank you for this comment. Title has been changed

2. Further references from literature are needed, e.g. bellow:

Wu, L., Yu, Z., Liu, C., Ma, Y., Huang, Y., Wang, T., Yang, L., Yan, H. and Liu, W., 2021. Microstructure and tensile properties of aluminum powder metallurgy alloy prepared by a novel low-pressure sintering. Journal of Materials Research and Technology, 14, pp.1419-1429.

This article is very interesting and has been added to the references list.

Godbole, K., Bhushan, B., Murty, S.N. and Mondal, K., 2024. Al-Si controlled expansion alloys for electronic packaging applications. Progress in Materials Science, p.101268.

This article has also been added to the references list.

*Cuzacq, L., Atchi, I., Bobet, J.L., Lu, Y. and Silvain, J.F., 2024. Pressureless sintering of Al/diamond materials using AlSi12 liquid phase. Materials Letters, p.137788.

The authors should explain why the *Cuzacq, L…. paper wasn’t included in the list of References.

This paper was not included because it was not accepted when we submit this article to the journal. Now it is and it has been added

3. Scale bars should be added to all pertinent Figures - Figure 2 and Figure 3.

The scale bars were added to the corresponding figures.

4. The authors should elaborate on accuracy and repeatability of the measurements, when applicable, e.g. relative density and other properties.

For each characterization, the measurement has been made 3 times to ensure an accuracy and a repeatability of the results. A sentence has been added in the methodology part to mentioned that point.

5. The authors should elaborate on the characteristic defects (pores and cracks) found in the material/samples, please include cracks in your discussion; NDT methods to be used for characterizing the discontinuities/defects should be presented and discussed.

Thank you for this remark. We have tried different methods in order to characterized the porosity inside our material after sintering such as tomography and SEM micrographs and image analysis. However, we were not able to accurately characterized the porosities we have in our materials. It is wright that NDT can be used to characterized “big” porosities but the resolution of our apparatus was nor enough for sub-micron one. Also, even correlation between porosity level and thermal conductivity can be found in some papers, it is, in our knowledge, impossible to correlate the shape and size of the porosity with the thermal conductivity of the materials.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

It is very difficult to compare the results of electron microscopy (Fig.3) and X-ray phase analysis (Fig.4). This is especially true of the statement that "Qualitative assessment using XRD analysis confirmed the the presence of alumina (Al2O3) layers in the Al powders used (Figure 4)". For such a statement, it is necessary to provide EDA data  or element mapping. And the structural components (Al, Si, Al2O3) in Figure 3 are better indicated by the arrows.

Author Response

Review Round 2

Reviewer 1

It is very difficult to compare the results of electron microscopy (Fig.3) and X-ray phase analysis (Fig.4). This is especially true of the statement that "Qualitative assessment using XRD analysis confirmed the presence of alumina (Al2O3) layers in the Al powders used (Figure 4)". For such a statement, it is necessary to provide EDA data or element mapping. And the structural components (Al, Si, Al2O3) in Figure 3 are better indicated by the arrows.

Thank you for this remark. It is completely true. It is ended difficult to compare Fig 3 and Fig 4. However, Fig 3 is presented in order to show the microstructure of the fabricated samples. Resolution of EDX analysis (around one cubic micron) is not good enough to show nanometric details such as the alumina layers and the possible Si segregation. Also, the surface roughness, after cryofracture, is not optimum for such analysis. Therefore, Fig 4 is used to show the crystallographic phases present in our sample. Finally, we cannot clearly show the phases in the Fig 3 because the Al Oxide is known to be present on all the particle's surface and the Si after melting diffused in all the samples. For all these reasons we did not show the phases in the Fig 3.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have made the necessary revision. It is ready for publication.

Author Response

Review Round 2

Reviewer 1

It is very difficult to compare the results of electron microscopy (Fig.3) and X-ray phase analysis (Fig.4). This is especially true of the statement that "Qualitative assessment using XRD analysis confirmed the presence of alumina (Al2O3) layers in the Al powders used (Figure 4)". For such a statement, it is necessary to provide EDA data or element mapping. And the structural components (Al, Si, Al2O3) in Figure 3 are better indicated by the arrows.

Thank you for this remark. It is completely true. It is ended difficult to compare Fig 3 and Fig 4. However, Fig 3 is presented in order to show the microstructure of the fabricated samples. Resolution of EDX analysis (around one cubic micron) is not good enough to show nanometric details such as the alumina layers and the possible Si segregation. Also, the surface roughness, after cryofracture, is not optimum for such analysis. Therefore, Fig 4 is used to show the crystallographic phases present in our sample. Finally, we cannot clearly show the phases in the Fig 3 because the Al Oxide is known to be present on all the particle's surface and the Si after melting diffused in all the samples. For all these reasons we did not show the phases in the Fig 3.

Author Response File: Author Response.docx