Anisotropic Tensile and Compressive Strengths of Al–4 wt.%Cu Alloy Powder: Part 1—Effects of Compaction Loads and Heat Treatments

Round 1

Reviewer 1 Report

The study reports on the mechanical properties of Al-Cu alloy and the importance of reusing the material for cost-effective production. Some of the minor comments are as follows:

1) On page 2, 2.1: Show the elemental composition Al-4Cu alloy in tabular form

2) On page 44, 2.2: Eq 1 and 2 are missing the appropriate superscript and subscript. It needs revision.

3) Throughout the manuscript, a few sentences are repeated. Eg., sentences in 2nd paragraph on page 10. Please revise. 

4) Correct the typos throughout the manuscript

The grammar can be improved to increase the quality of the manuscript

Author Response

Reviewer(s)' Comments to Author:

Reviewer: 1

The study reports on the mechanical properties of Al-Cu alloy and the importance of reusing the material for cost-effective production. Some of the minor comments are as follows:

1) On page 2, 2.1: Show the elemental composition Al-4Cu alloy in tabular form.

AUTHORS: The Reviewer’s suggestion is an excellent comment. However, it was decided among the coauthors that text is comprehensible method. Also, it is widely used in literature. Based on this decision, unfortunately, we have declined this modification.

2) On page 44, 2.2: Eq 1 and 2 are missing the appropriate superscript and subscript. It needs revision.

AUTHORS: The Authors congratulate the Reviewer’s suggestion. This problem has been solved. The modification are yellow highlighted.

3) Throughout the manuscript, a few sentences are repeated. Eg., sentences in 2nd paragraph on page 10. Please revise.

AUTHORS: The Reviewer’s suggestion was adopted. An extensive English writing was meticulously provided. All modifications are yellow highlighted.

4) Correct the typos throughout the manuscript

AUTHORS: The Reviewer is correct. A great number of corrections were provided.

Reviewer 2 Report

The paper provides a rather extended research investigation on a typical casting Al alloy system. Although the intents of the paper are specified in details, the article does not succeed in most of its aims.

It is not clear why authors introduce the concept of materials' recyclability and then the powders are obtained (and processed) in very peculiar conditions which don't represent the normal industrial processing.

Several studies in literature (more focused in "proper" systems used in the Powder Metallurgy of Al alloys than ref [18-20]) report the importance of the correct granulometry in the Press and sinter of Al systems.

Why the level of O2 hasn't been measured (for instance by means of LECO method)?

The characterization of the powder is not complete. It is very limiting to provide the results obtained only by means of SEM observation

Which kind of standard (for P/M) has been applied for the determination of density?

Why no thermal analysis have been used for the determination of the correct sintering T? Or, at least, why no reference to a "proper" system (research or commercial) has been adopted?

Results of the tensile testing are definetely TOO low to be event taken into account!!!

Under these premises the conclusion

"Recycled powder particles from conventional ma-chining processes can potentially be used, allowing for the production of compo-nents with specific mechanical requirements through careful compaction planning and treatments."

does not have any sense!

Proof reading advised

Author Response

Reviewer: 2

1. The paper provides a rather extended research investigation on a typical casting Al alloy system. Although the intents of the paper are specified in details, the article does not succeed in most of its aims.

AUTHORS: The Reviewer is correct. Modifications are provided.

2. It is not clear why authors introduce the concept of materials' recyclability and then the powders are obtained (and processed) in very peculiar conditions which don't represent the normal industrial processing.

AUTHORS: The Reviewer is correct. The sentence was revised and it was also explained this peculiar condition. These modifications are yellow highlighted.

3. Several studies in literature (more focused in "proper" systems used in the Powder Metallurgy of Al alloys than ref [18-20]) report the importance of the correct granulometry in the Press and sinter of Al systems.

AUTHORS: The Reviewer is correct. This block of references was deleted when concerning this specific comment.

4. Why the level of O2 hasn't been measured (for instance by means of LECO method)?

AUTHORS: The Reviewer is correct. However, Authors have not domain in technique/method and adequate equipment to carry out these measurements.

5. The characterization of the powder is not complete. It is very limiting to provide the results obtained only by means of SEM observation

AUTHORS: The Reviewer’s comment is correct. Additionally, it can also be observed that measurements of the power size distributions and XRD measurements were also carried out.

6. Which kind of standard (for P/M) has been applied for the determination of density?

AUTHORS: This is a good comment. Archimedes’ principle was adopted. Based on this, ASTM standard is mentioned/cited.

7. Why no thermal analysis have been used for the determination of the correct sintering T? Or, at least, why no reference to a "proper" system (research or commercial) has been adopted?

AUTHORS: This is another excellent Reviewer’s comment. Based on a great number of previously reported articles and based on the expertise in the Al-based alloy treat treatment, it is widely recognized that temperature utilized. On the other hand, there exists the sintering time, which surely will provide another paper. However, it is adopted a minimal interval sintering time based on the fact that optimizing operational parameters are focused. Additionally, concerning to the mentioned sentence, references are cited/included. These modifications are yellow highlighted.

8. Results of the tensile testing are definetely TOO low to be event taken into account!!!

AUTHORS: The Reviewer is also correct. This attained results is expected and predictable based on previously reported articles. These are also mentioned in this study. However, this was confirmed and the compressive tests complemented, indicating another possible application. The modifications concern to sentences are yellow highlighted.

9. Under these premises the conclusion

"Recycled powder particles from conventional ma-chining processes can potentially be used, allowing for the production of compo-nents with specific mechanical requirements through careful compaction planning and treatments."does not have any sense!

AUTHORS: The Reviewer is also correct. The sentences were modified (yellow highlighted texts).

Reviewer 3 Report

The authors studied the influence of different pressing directions on the strength of powder metallurgy parts. The initial powder can be waste from machining, turning or casting, which is cost-effective and environmentally friendly. The article provides enough experimental data, and the logic of the demonstration process is rigorous. The language is fluent and there are almost no mistakes.  Therefore, I suggest receiving it in the present form.

Author Response

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Reviewer: 3

The authors studied the influence of different pressing directions on the strength of powder metallurgy parts. The initial powder can be waste from machining, turning or casting, which is cost-effective and environmentally friendly. The article provides enough experimental data, and the logic of the demonstration process is rigorous. The language is fluent and there are almost no mistakes.  Therefore, I suggest receiving it in the present form.

AUTHORS: Authors thank Reviewer’s comment and evaluation.

Reviewer 4 Report

Please find my detailed comments and feedback in the attached document (PDF). Thank you.

Comments for author File: Comments.pdf

The overall quality of English language usage in this article is quite good. However, there are a few areas where improvement is needed. Some sentences are pretty long and complex. Also, consider replacing phrases like "to make clear" with "to clarify" or "to illustrate." 

Author Response

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Reviewer: 4

The overall quality of English language usage in this article is quite good. However, there are a few areas where improvement is needed. Some sentences are pretty long and complex. Also, consider replacing phrases like "to make clear" with "to clarify" or "to illustrate."

I appreciate the authors for this study, which delves into the mechanical behavior of Al-Cu alloy powders and sheds light on the influence of compaction direction and heat treatment on the mechanical properties of these alloys, demonstrating some scientific rigor. Besides, looking into the manuscript write-up, I strongly encourage the authors to carefully consider these suggestions as they further refine their work for possible acceptance in ‘MDPI Metals’.

1. In the abstract, consider providing a brief statement of the research's significance and potential practical applications. Additionally, the abstract includes specific numerical results (e.g., the percentage increase in densification).

AUTHORS: Authors congratulate the Reviewer’s comment and suggestions provided. The modifications are adopted and these are yellow highlighted.

2. In the introduction section, emphasize the significance of studying the mechanical behavior and anisotropy of Al-Cu alloy powders, and also emphasizes the gaps in current knowledge regarding the mechanical behavior of Al-Cu alloy powders and the importance of addressing these gaps for practical applications.

AUTHORS: The Reviewer is correct. Modifications are provided and these are yellow highlighted.

3. In section 2, justify the rationale for selecting the specific compaction pressures tested. Were these pressures chosen based on theoretical predictions, prior research, or practical manufacturing constraints?

AUTHORS: The Reviewer is also correct. New sentences are included, and these are yellow highlighted.

4. Include information about the sample size and the number of replicates to evaluate the statistical significance ofthe findings.

AUTHORS: This suggestion is provided when number of samples are utilized. New sentences are included and these are yellow highlighted.

5. Include a subsection devoted to the characterization techniques used for morphological analysis (SEM analysis). Additionally, provide justification for the choice of the specific compaction pressures tested.

AUTHORS: Although a new subsection concerning to SEM analysis was not adopted, the Reviewer’s suggestion is adopted, and new sentences are yellow highlighted.

6. Clarification is needed regarding the units used for densification values.

AUTHORS: This suggestion is adopted. New sentences are adopted in order to explain this matter. Percentage is based on the theoretical values (in g/cm³).

7. Provide more detailed descriptions of the trends observed in the figures (e.g., how the anisotropy ratios change with compaction pressure).

AUTHORS: This suggestion is adopted. These modifications are yellow highlighted.

8. Explain the physical significance of the Heckel equation parameters (A and B) and how they relate to the experimental results. Additionally, specifying the units of the variables in the equation would add clarity.

AUTHORS: This suggestion is adopted. The modifications are yellow highlighted.

9. Discussion on the anisotropy ratio could be expanded to include potential reasons behind the observed trends, such as the role of particle morphology and compaction pressure.

AUTHORS: The Reviewer is correct. The modifications are adopted and these are yellow highlighted.

10. Provide more context for the logarithmic equation (UCS = 64 ln(UTS) - 80) and its significance. How does this equation contribute to understanding the relationship between tensile and compressive strength in these materials?

AUTHORS: The Reviewer is correct. New sentence are yellow highlighted.

11. Remove those shadow effects in Figures. {Blue lines in Figures 2 (c) & (d); Fig 3 (c); Fig 4 (e)}. Lines in Figure 4 (a, b, c & d) and 10 are not legible; a colorful representation is recommended.

AUTHORS: The Reviewer is correct. These modifications are adopted in proof version when final processing stage.

12. Several references (Ref 3-7, 20, 22, 26, 27, 30, 31, 35) appears to be outdated. Replace them with more recent and pertinent sources to strengthen the validity of the content. I suggest considering the inclusion of a couple or three references from 'MDPI Metals', which add credibility to the manuscript.

AUTHORS: The Reviewer is correct. The modifications are possibly adopted.

Reviewer 5 Report

The authors made research on  tensile and compressive strengths of Al–4wt.%Cu alloy powder: Part 1. however a major correction is required to enhance the quality of manuscript

1.abstract needs to be modified with scientific values 

2. The novelty  and the materials processing methods of present investigation needs to be improved with similar findings 

3. The result and discuss needs to be optimized as per the need for the current investigation and wettability, interface reaction, strengthening mechanism and effect of grain refinement between the immixture needs to discusses 

4.  How can the present research differs from existing findings needs to included before conclusion and it must related to need for applications 

5. Conclusion needs to optimized with previous with scientific values

Author Response

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Reviewer: 5

The authors made research on  tensile and compressive strengths of Al–4wt.%Cu alloy powder: Part 1. however a major correction is required to enhance the quality of manuscript

1.abstract needs to be modified with scientific values 

AUTHORS: As also indicated by other Reviewers, the modifications are adopted and these are yellow highlighted.

2. The novelty  and the materials processing methods of present investigation needs to be improved with similar findings 

AUTHORS: The Reviewer is correct. Some modifications are adopted and these are yellow highlighted.

3. The result and discuss needs to be optimized as per the need for the current investigation and wettability, interface reaction, strengthening mechanism and effect of grain refinement between the immixture needs to discusses 

AUTHORS: The Reviewer is correct. Possible modifications concerning to matter are adopted and these are yellow highlighted.

4. How can the present research differs from existing findings needs to included before conclusion and it must related to need for applications 

AUTHORS: The Reviewer is correct. The related texts were verified and modified adequately, as yellow highlighted.

5. Conclusion needs to optimized with previous with scientific values

AUTHORS: The Reviewer is correct. As also requested by other Reviewers, the Conclusion section was meticulously revised and improved.

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Round 2

Reviewer 2 Report

Authors answered to the questions/comments or declared that they cannot perform the requested analysis

Reviewer 4 Report

Accept in present form