The Influence of La and Ce on Microstructure and Mechanical Properties of an Al-Si-Cu-Mg-Fe Alloy at High Temperature

Round 1

Reviewer 1 Report

The reviewer comments of the paper «The influence of La and Ce on mechanical properties of an Al-Si-Cu-Mg-Fe alloy at high temperature»

- Reviewer

The authors presented an article «The influence of La and Ce on mechanical properties of an Al-Si-Cu-Mg-Fe alloy at high temperature». In general, the article is interesting and written at a good scientific level. However, there are several points in the article that require further explanation.

Comment 1:

Overall, the introduction is well written. However, at the end of the introduction, briefly list what has been done in each section of the article. It is useful to add an article: doi: 10.1016/j.jmrt.2020.10.001

Comment 2:

It is better to use "Copper (Cu)" instead of "Cu" in the text of the article. The same goes for other elements. In Table 2, I suggest doing the same. At least if such elements are encountered for the first time in the text of the article.

The tables in Figure 4 must be formatted according to the MDPI requirements.

The text in Figure 5 in the corner is illegible. We need to improve the quality of the drawings. It is also helpful to add a scale bar.

Specify the title of Figure 9. What is the model?

Comment 3:

It will be useful to add a section of Nomenclature in which to sign all the physical quantities and abbreviations encountered in the article. There are many physical quantities in the text and such a section will help to find the description of the necessary element.

For example,

???        : Matrix material yield point

Al-MMC : Al-based metal matrix composite

Cu          : Copper

etc.

Comment 4:

Conclusions.

Add quantitative and qualitative work results.

In addition, it is necessary to more clearly show the novelty of the article and the advantages of the proposed method. What is the difference from previous work in this area? Show practical relevance. Conclusions should reflect the purpose of the article.

Comment 5:

It is probably useful to add microstructure research to the title of the article too.

 

After major changes can an article be considered for publication in the "Metals".

 

Author Response

Reviewer 1

• Overall, the introduction is well written. However, at the end of the introduction, briefly list what has been done in each section of the article. It is useful to add an article: doi: 10.1016/j.jmrt.2020.10.001

Reply: Thank you for the suggestion.

Action: The suggested paper was added to the references and the following text was added“Hard phases such as SiC/Cr particulates can increase friction and surface hardness making them ideal for brake rotor applications”

• It is better to use "Copper (Cu)" instead of "Cu" in the text of the article. The same goes for other elements. In Table 2, I suggest doing the same. At least if such elements are encountered for the first time in the text of the article.

Reply: Thank you for the suggestion improvement.

Action: the full name of the element used int the article are labeled for the first time in the text, In Table 2, the version of the element was also changed. (14-16) (66-67)(137-138)

• The tables in Figure 4 must be formatted according to the MDPI requirements.

Reply: Thank you for noting this discrepancy in formatting

Action: The picture was changed to adhere to the MDPI requirements (200-201）

• The text in Figure 5 in the corner is illegible. We need to improve the quality of the drawings. It is also helpful to add a scale bar.

Reply: Thank you for the suggestion

Action: The background and font was changed to improve visibility and clarity. (221-224)

• Specify the title of Figure 9. What is the model?

Reply: Thank you for the suggestion

Action: Frigure 9 caption was clarified and changed from " Predicted versus actual values from the modelling. Red points are the data omitted in the fitting. " to " Predicted versus actual values from the model, equations (1-4). Red points are the data omitted in the fitting."

• It will be useful to add a section of Nomenclature in which to sign all the physical quantities and abbreviations encountered in the article. There are many physical quantities in the text and such a section will help to find the description of the necessary element
  For example,
  ???        : Matrix material yield point
  Al-MMC : Al-based metal matrix composite
  Cu          : Copper

Reply: Thank you for the suggestion. The paper is primarily an experimental paper and as such the elements used in the model are regarded as limited and thus seen as sufficiently explained in the text.

Action: None taken

• 
  Add quantitative and qualitative work results.

Reply: Thank you for the suggestion.

Action: In the discussion and conclusion part, qualitative work results have been added. (365-380)

• In addition, it is necessary to more clearly show the novelty of the article and the advantages of the proposed method. What is the difference from previous work in this area? Show practical relevance. Conclusions should reflect the purpose of the article.

Reply: Thank you for the suggestion.

Action: This is stressed as a special section in the Conclusions as:

1. At room temperature, the UTS significant drop with the additions of (Ce and La), the 4% RE addition was the lowest, which is 59% strength lost compared with none RE addition. Due to the crack formed in the coarse phases Al11(Ce, La)3, the stress concentration was arising from the high aspect ratio plate-like phases.
2. At 200oC the 1%(Ce and La) additions got the highest UTS strength, even better than the room temperature strength and 6.7% higher than the none RE addition. That is because the smaller size precipitates improve stress distribution then improve strength.
3. At 300oC the 2% (Ce and La) additions got the highest 115.36 MPa UTS strength, which is 54.63% strength improved compared with none RE addition. A network structure Al11(Ce, La)3 appears, through a distributed load-bearing effect improve the high-temperature strength.
4. At 400oC the 4% (Ce and La) additions got the highest 47.82 MPa UTS strength, which is 108.91% strength improved compared with none RE addition. Although the large plate-like morphology of the primary precipitated Al11(Ce, La)3 phase harms the room temperature property, but due to the high temperature stable phases could distribute stress, the high-temperature strength improved

• It is probably useful to add microstructure research to the title of the article too.

Reply: Thank you for the suggestion. The microstructure is a small but important part of the study and the main focus is still the effect of RE on mechanical properties. The morphological effects on properties and the rapid decrease in ductility with the primar porecipitation allows us to include the microstructure in the title.

Action: The title was changed to “The influence of La and Ce on microstructure and mechanical properties of an Al-Si-Cu-Mg-Fe alloy at high temperature”

Author Response File: Author Response.pdf

Reviewer 2 Report

Very interesting article describing the influence of La and Ce on properties of Al alloys. The research is particularly valuable due to the need to reduce the weight of vehicles and increase their load capacity, which significantly affects the efficiency of transport and protects the environment. In the work, the authors described in detail the methodology of both the preparation of material for research as well as individual research methodologies. It should be stated that the scope of research and their methodology are correctly selected and the obtained results are properly described. An important supplement to the research would be the identification of the revealed phases by X-ray diffraction on a TEM microscope. The conducted, very detailed analysis of the results fully justifies the conclusions drawn. In my opinion, the work may be published in its current form in the "Metals" journal

Author Response

Reviewer 2

• Very interesting article describing the influence of La and Ce on properties of Al alloys.The research is particularly valuable due to the need to reduce the weight of vehicles and increase their load capacity, which significantly affects the efficiency of transport and protects the environment. In the work, the authors described in detail the methodology of both the preparation of material for research as well as individual research methodologies. It should be stated that the scope of research and their methodology are correctly selected and the obtained results are properly described. 

Reply: Thank you for your recognition of my article.

Action: No action required

• An important supplement to the research would be the identification of the revealed phases by X-ray diffraction on a TEM microscope.

Reply: Thank you for your kind suggestion.

Action: This is not practically possible but will be included in future studies of this topic

• The conducted, very detailed analysis of the results fully justifies the conclusions drawn.In my opinion, the work may be published in its current form in the "Metals" journal

Reply: Thank you very much for your recognition of my article, I will continue to work hard.

Action: None required

Author Response File: Author Response.pdf

Reviewer 3 Report

The paper "The influence of La and Ce on mechanical properties of an Al-Si-Cu-Mg-Fe alloy at high temperature " by A. Du and co-authors needs some major improvements in the Results and Discussion section.

More specifically, Section 3.3.2 and 3.4 must be deeply revised and rephrased: it is difficult to correctly understand how the mechanical performance of the different alloys varies with temperature and how La and Ce additions are contributing to the variations in YS, UTS and A%. The additions obviously have combined effects, but such influence seems just roughly explained or treated in the text.

I believe this invariably leads to the "data cleaning" for alloy A4 (lines 323-326), which appears to be quite arbitrary. Why including YS data at the highest temperatures and not UTS and elongation? Which contribution did you link to alloys' matrix softening with temperature in your model? The approach used by Ceschini and al. is well known and somewhat correct, but I think that the authors' investigation should go more in detail.

Minor text revisions are also needed in the other sections, especially in the Conclusions.

Author Response

Reviewer 3

• The paper "The influence of La and Ce on mechanical properties of an Al-Si-Cu-Mg-Fe alloy at high temperature " by A. Du and co-authors needs some major improvements in the Results and Discussion section.

Reply: Thank you for the suggestion.

Action: In the discussion and conclusion part, qualitative work and strengthening mechanism results have been added. (365-380)

• More specifically, Section 3.3.2 and 3.4 must be deeply revised and rephrased: it is difficult to correctly understand how the mechanical performance of the different alloys varies with temperature and how La and Ce additions are contributing to the variations in YS, UTS and A%. The additions obviously have combined effects, but such influence seems just roughly explained or treated in the text.

Reply: Thank you for the suggestion.

Action: Section 3.3.2 and 3.4 have been revised and rephrased, In 3.3.2, we focus on the effect of RE on UTS of materials, theoretical analysis is added in 3.3.2. The data of YS and A% are used in 3.4 simulation analysis.

• I believe this invariably leads to the "data cleaning" for alloy A4 (lines 323-326), which appears to be quite arbitrary. Why including YS data at the highest temperatures and not UTS and elongation?

Reply: Thank you for the suggestion.

Action: I make a mistake on the number of UTS of alloy A4, it has been corrected. (255-256)

• Which contribution did you link to alloys' matrix softening with temperature in your model? The approach used by Ceschini and al. is well known and somewhat correct, but I think that the authors' investigation should go more in detail.

Reply: The current investigation focus on the influence of the hard and larger stable phases. The effects that are related to the matrix phase were not of primary interest as these relate more to the 5 strengthening mechanisms for conventional ally development. These are partly related to the balance between precipitation hardening and solution hardening where the fine precipitates related to Mg₂Si and Al₂Cu may influence. This may be partially be counteracted by a precipitation of Si due to supersaturation of Si in the phase and the precipitation of Si, It is also related to the Peierl-Nabarro term of the strengthening where thermal activation may play a role in the softening mechanism primarily through the reduction of the Shear modulus. These effects were in the modelling work attributed for in equation (1) in the term .

Action: we added the new sentence “As we know with the increase of temperature, the alloy matrix begins to soften. Material thermal softening is mainly related to precipitation hardening and solution hardening, as well as the Peierl-Nabarro stress. The Peierls stress is called lattice friction which is meain resistance to dislocation motion, the fine precipitates Mg2Si and Al2Cu prevent dislocation movement, So as to play the role of high temperature resistance. we use the RE free material as a base line, these effects were in the modelling work attributed for in equation (1) in the term .”（295-300）

• Minor text revisions are also needed in the other sections, especially in the Conclusions.

Reply: Thank you for the suggestion.

Action: In the discussion and conclusion part, qualitative work and strengthening mechanism results have been added. (365-380)

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have improved the article according to the comments. However, it is useful to improve the quality and resolution of figures 2, 4, 5 before becoming published.

Author Response

1) The authors have improved the article according to the comments. However, it is useful to improve the quality and resolution of figures 2, 4, 5 before becoming published Reply: Thank you for the suggestion. Action: The quality of figure 2,4,5 has been improved to 1170*780 pixels

Reviewer 3 Report

Please, correct as follows:

• line 24: "stain" should be "strain"
• line 84-85: "Usually, the alloying elements Nickel (Ni), Cu and Mg have been used"
• line 206: "Figure 5.... of Al11(Ce,La)3." The sentence is difficult to understand and must be rephrased.
• line 212: "fund" should be "found"
• line 222-224: I would delete this sentence, as it does not add any further information
• line 236: "a more network" should be "a more interconnected network"
• line 237: "therefor" should be "therefore"
• line 239: "or large plates" should be "of large plates"
• line 242-243: "The addition of... grain refinement" sentence should be rephrased
• line 251: "approximated" should be "approximately"
• line 253: "Measure... Feret diameter" sentence should be rephrased
• Table 4: Hardness values are repeated in the right part of each series of data. Please, write them just once.
• line 274-275: rewrite sentence "The presence... primary precipitation of Al11(Ce,La)3", as it is difficult to understand
• line 281-293: please, rephrase the whole paragraphs, as they are very difficult to read
• line 303: "the addition" should be "the additions"
• line 320: "additional" should be "additions"
• line 352: "these" should be "the"
• Figure 9: Specify the name and unit of the axes and eliminate the legend
• line 371: "(Ce and La) additions did affect the mechanical properties due to the precipitation of the Al11(Ce,La)3 phase."
• line 373-389: please, check typos
• line 392: "and thus also to keep" should be "and thus also kept"

Author Response

Reviewer 3

• The paper

line 24: "stain" should be "strain"

line 84-85: "Usually, the alloying elements Nickel (Ni), Cu and Mg have been used"

line 212: "fund" should be "found"

line 222-224: I would delete this sentence, as it does not add any further information

line 236: "a more network" should be "a more interconnected network"

line 237: "therefor" should be "therefore"

line 239: "or large plates" should be "of large plates"

line 251: "approximated" should be "approximately"

Table 4: Hardness values are repeated in the right part of each series of data. Please, write them just once.

line 303: "the addition" should be "the additions"

line 320: "additional" should be "additions"

line 352: "these" should be "the"

line 371: "(Ce and La) additions did affect the mechanical properties due to the precipitation of the Al11(Ce,La)3 phase."

line 392: "and thus also to keep" should be "and thus also kept"

Reply: Thank you for the suggestion.

Action: all the words have been chenged

(1)    line 206: "Figure 5.... of Al11(Ce,La)3." The sentence is difficult to understand and must be rephrased.

Reply: Thank you for the suggestion.

Action: line 206: "Figure 5.... of Al11(Ce,La)3." changed from " Figure 5, together with the XRD results, Figure 3, and the EDS analysis, Figure 4, it can be concluded that the plate-like phase predominantly consists of Al₁₁(Ce, La)₃." to " The element mapping, Figure 5, displays a bright white plate-like phase that coincides with the Ce and La distribution, suggesting that it is Ce and La containing. .. The EDS analysis, Figure 4 of this white plate-like phase shows that it is an an aluminium-rich phase with an equi-atomic contribution from Ce and La. Together with the XRD results, Figure 3, where the phase Al₁₁(Ce, La)₃ was confirmed, it can be concluded that the plate-like phase is Al₁₁(Ce, La)₃ . It can also be seen that the Ni distribution partially coincides with the Ce and La distribution, supporting thethe EDS measurements that  presence for Ni in the Al₁₁(Ce, La)₃.-plates was a correct interpretation and not an artefact, thus Ni is suggested to dissolve into Al₁₁(Ce, La)₃."

(2) line 242-243: "The addition of... grain refinement" sentence should be rephrased

Reply: Thank you for the suggestion. Even though grain refinement is an important matter it is not central to the paper. The SDAS measure is more relevant to cast Alloys.

Action. Sentence removed

Action: line 242-243: "The addition of... grain refinement" sentence should be rephrased changed from " The addition of... grain refinement ." to " The addition of (Ce and La) result in heterogeneous nucleation of Al₁₁(Ce, La)₃ which is expected to grain refinement of the matrix."

(3) line 253: "Measure... Feret diameter" sentence should be rephrased  add a refference

Reply: Thank you for the suggestion.

Action: changed from " Measure the length according to Feret diameter." to "  The size measurement was made according to Feret diameter principle."

(4) line 274-275: rewrite sentence "The presence... primary precipitation of Al11(Ce,La)3", as it is difficult to understand

Reply: Thank you for the suggestion.

Action: changed from " The presence... primary precipitation of Al11(Ce,La)3." to " The presence of cracks will,together with the stress concentration arising from the high aspect ratio plate-like primary precipitation of Al₁₁(Ce, La)₃ result in a more brittle material ."

(5) line 281-293: please, rephrase the whole paragraphs, as they are very difficult to read

Reply: Thank you for the suggestion.

Action: changed from " In Figure 6(c) the Al₁₁(Ce, La)₃ phases appears to form a network structure that may support through a distributed load-bearing support, which becomes important at elevated temperature as they are stable at this temperature. The smaller size precipitates and the absence of cracks in the particles at lower (Ce and La) additions. Figure6(b-c) show the phases dispersed in the matrix evenly, which means stress could distribute at the intermetallic interface improved stress distribution and improve strength. Table 4 shows that the tensile strength of EN AC 46000 is 110MPa at 300^oC and 20MPa at 400^oC. The formation of a network is why the tensile strength at 300^oC and 400^oC is high than that of the EN AC 46000 alloy.

At 400^oC the addition of 4% (Ce and La) in the alloy, the UTS strength increased from 22.89MPa to 47.82MPa over 108.9% compared with none (Ce and La) addition. Although the large plate-like morphology of the primary precipitated Al₁₁(Ce, La)₃ phase harms the room temperature property, but due to the high temperature stable phases could distribute stress, the high-temperature strength improved." to " Figure 6 (b-c) show the phases dispersed in the matrix, the smaller size phases precipitates and the absence of cracks in the particles at lower (Ce and La) additions. The load-bearing theory play an important ruler in the improvement of strength, which means stress could distribute at the intermetallic interface and improved stress distribution. Table 4 shows that the tensile strength of EN AC 46000 is 110MPa and 20MPa at 300^oC, 400^oC respectively. The tensile strength of A3 alloys (2% Ce and La) at 300^oC and 400^oC is high than that of the EN AC 46000 alloy. The Al₁₁(Ce, La)₃ phases appear to form a network structure and the structure are stable at elevated temperature, that may improve high temperature property.

At 400^oC the addition of 4% (Ce and La) in the alloy, the UTS strength increased from 22.89MPa to 47.82MPa over 108.9% compared with none (Ce and La) addition. Although the large plate-like morphology of the primary precipitated Al₁₁(Ce, La)₃ phase harms the room temperature property, but due to the high temperature stable phases could distribute stress, the 400^oC strength improved.

(6) Figure 9: Specify the name and unit of the axes and eliminate the legend

Reply: Thank you for the suggestion.

Action: the name and unit of the axes has been add

(7) line 373-389: please, check typos

Reply: Thank you for the suggestion.

Action: changed from "

1. Squeeze casting could be used to produce a sound material quality for all compositions
2. (Ce and La) addition primarily resulted in the precipitation of Al₁₁(Ce, La)₃ and a possible modification of the α-Al₁₅(Fe, Mn)₃Si₂ as Chinese script precipitates were absent.
3. Al₁₁(Ce, La)₃ precipitated, as a primary precipitate, in small amounts at 2% (Ce and La) additions. At 4% (Ce and La) addition a fully developed coarse plate-like Al₁₁(Ce, La)₃ precipitated
4. (Ce and La) additions did affect the mechanical properties due to the precipitation of Al₁₁(Ce, La)₃
5. At room temperature, the UTS significant drop with the additions of (Ce and La), the 4% RE addition was the lowest, which is 59% strength lost compared with none RE addition. Due to the crack formed in the coarse phases Al₁₁(Ce, La)₃, the stress concentration was arising from the high aspect ratio plate-like phases.
6. At 200^oC the 1%(Ce and La) additions got the highest UTS strength, even better than the room temperature strength and 6.7% higher than the none RE addition. That is because the smaller size precipitates improve stress distribution then improve strength.
7. At 300^oC the 2% (Ce and La) additions got the highest 115.36 MPa UTS strength, which is 54.63% strength improved compared with none RE addition. A network structure Al₁₁(Ce, La)₃ appears, through a distributed load-bearing effect improve the high-temperature strength.
8. At 400^oC the 4% (Ce and La) additions got the highest 47.82 MPa UTS strength, which is 108.91% strength improved compared with none RE addition. Although the large plate-like morphology of the primary precipitated Al₁₁(Ce, La)₃ phase harms the room temperature property, but due to the high temperature stable phases could distribute stress, the high-temperature strength improved.
9. Analysis through modelling on the nature of the strengthening mechanisms revealed that the dominant contribution to yield strength was the load-bearing mechanism.
10. Similarly, elastic modulus mismatch contributed to hardening and thus also kept the tensile strength high.

" to "

1            Squeeze casting could be used to produce a sound material for all compositions

2          (Ce and La) addition primarily resulted in the precipitation of Al₁₁(Ce, La)₃ and a   possible modification of the α-Al₁₅(Fe, Mn)₃Si₂, as Chinese script precipitates were absent.

3       Al₁₁(Ce, La)₃ precipitated, as a primary precipitate, in small amounts at 2% (Ce and La)    additions. At 4% (Ce and La) addition a fully developed coarse primary precipitated plate-like Al₁₁(Ce, La)₃ formed.

4            (Ce and La) additions did affect the mechanical properties due to the precipitation of   Al₁₁(Ce, La)₃ phase.

a     At room temperature, the UTS significant drop with the additions of (Ce and La).        The 4% RE addition showed the biggest drop of 59% strength compared with the material without RE addition. This drop was due to the cracks formed in the coarse primary Al₁₁(Ce, La)₃-phases, the stress concentration was arising from the high aspect ratio plate-like phases.

b    At 200^oC the 1%(Ce and La) additions showed the highest UTS, also at  room temperature strength. The improvement at 200^oC was 6.7% higher compared to the material without  RE addition. The reason for the improvement was because the smaller size precipitates to carry part of the load without causing detrimental stress concentrations.

c     At 300^oC the 2% (Ce and La) additions showed the highest UTS (115.36 MPa.) , which is 54.63% strength improvement compared to the  RE-free material. A network structure of Al₁₁(Ce, La)₃ appears, that through a distributed load-bearing effect improved the high-temperature strength.

d      At 400^oC the 4% (Ce and La) additions showed the highest UTS  with 47.82 MPa., which   is a 108.91% strength-improvement compared without RE addition. Although the large plate-like morphology of the primary precipitated Al₁₁(Ce, La)₃ phase significantly hampers the room temperature UTS, the high temperature stable phases could carry load and qimprove the high-temperature strength.

5      Analysis through modelling the nature of the strengthening mechanisms revealed that the dominant contribution to yield strength was the load-bearing mechanism.

6      Similarly, elastic modulus mismatch contributed to hardening and thus also kept the tensile strength high (UTS)."

Author Response File: Author Response.pdf