Alternative Liquid-Assisted Sintering of Al/Cu Composites Using Selected Powders of As-Cast Al-Zn Alloy

Round 1

Reviewer 1 Report

Thanks to the authors for the work done to obtain a large amount of data.
However, the results stated in the article raise a number of questions.
1) What is the actual economic effect of using this method? It is necessary to obtain a powder of the desired fraction, it is necessary to sinter at sufficiently high temperatures for 3 hours, and the mechanical properties of this alloy leave much to be desired.
2) Please give a more visual comparison of the mechanical properties of the samples obtained by your method in comparison with the samples obtained by casting.
3) Why was the structure not stabilized to assess the hardness? Solution quenching and aging typical for this type of alloy

Author Response

Dear Reviewer, 

We are grateful for yours comments and suggestions. Find below are our answers to your questions.

Q1: Thanks to the authors for the work done to obtain a large amount of data. However, the results stated in the article raise a number of questions. 1) What is the actual economic effect of using this method? It is necessary to obtain a powder of the desired fraction, it is necessary to sinter at sufficiently high temperatures for 3 hours, and the mechanical properties of this alloy leave much to be desired.

AUTHORS: The comment provided by Reviewer is correct. In order to elucidate this point, a new sentence is included, as yellow highlighted:

“This suggests that the proposed alloy and the adopted liquid-assisted sintering are promised to a manufacturing route. Both environmentally-friendly and economical aspects are associated (no foundry is occurring and recycled powder or rejection from rolling can be utilized). Besides, a low energy consumption, without a melting point be reached.”

Q2: Please give a more visual comparison of the mechanical properties of the samples obtained by your method in comparison with the samples obtained by casting.

AUTHORS: Although the authors agreed with Reviewer’s comment, it was adopted a new sentence with 5 new references to permit this comparison. This new sentence is yellow highlighted:

 “It can be seen that the hardness trends to stabilize probably at 500 days (~100 HV). Although a decrease tendency in thehardness is attributed to the overaging occurring in Al-Cu-based alloys, based on the proposed Equation 1, it is not possible to predict this occurrence. From the above-obtained experimental results, it can be observed that the mechanical behavior (UTS) and hardness of the Al6Cu5Zn alloy are similar to those of the as-cast Al alloys [40, 41, 42, 43, 44, 45].This suggests that the proposed alloy and the adopted liquid-assisted sintering are promised to a manufacturing route. Both environmentally-friendly and economical aspects are associated (no foundry is occurring and recycled powder or rejection from rolling can be utilized). Besides, a low energy consumption, without a melting point be reached.”

Q3: Why was the structure not stabilized to assess the hardness? Solution quenching and aging typical for this type of alloy.

AUTHORS: The Reviewer is correct. However, it is commonly used an aging with UTS at aging with hardness to express the variation of the properties with aging period. This is provided in a simple “blank”(as-cast) and those heat-treated during distinctive aging period, as provided in this investigation. 

Reviewer 2 Report

Dear Authors,

The work presented is of great interest in the creation of composite intermetallic materials. The Al6Cu5Zn alloy obtained as a result of experimental work is of interest as an experimental example of the process of creating a composite alloy with improved mechanical properties and at the same time a more economical manufacturing process. 
Of particular interest of the presented work is a detailed study of the effect of aging on the change in hardness of the resulting composite alloy.

Author Response

Dear Reviewer, 

Reviewer 3 Report

In the manuscript entitled “Alternative Liquid Assisted-Sintering of Al/Cu composites using selective powders of as-cast Al-Zn alloy”, the author demonstrated a way of synthesizing noncommercial Al6Cu5Zn alloy by PM. There exists a lot of uncertainties, which need to be substantially revised. Detailed comments are made below:

1. The author said that “Cu powder particles are easily identified since their particles are brighter than other particles due to the SEM technique used (secondary electron technique) and higher molecular weight.” Since the secondary electron is not sensitive to the atomic mass, this narrative may not be right. Please provide a more convincing reason for this phenomenon.
2. The author mentioned that “the irregular sizes of powders facilitate the rearrangement between particles, and consequently, the porosity after sintering is decreased.” Have the author compared their results with spherical particles?
3. What is “The energy to activate the diffusion mechanisms is also increased.”? Which kind of energy does it refer to? It is true that diffusion is related to temperature, but there does not exist the activation energy.
4. Please label different phases in the SEM images. It seems there are several phases in the alloys.
5. And also, why does the alloy sintered at higher temperatures look less uniform than the low temperature sintered alloy?
6. Because the alloy is brittle, the justification for the comparison of their strength is insufficient. All the samples break before yielding!
   Hardness data is more useful for the purpose.
7. If the author sinters the alloy for a longer time, it is possible to make a fully dense alloy?
8. The author mentioned that “atomic diffusion of Cu is intense”. Technically, it is right. But some calculations on the diffusion distance are needed.

Author Response

Dear Reviewer, 

We are grateful for yours comments and suggestions. Find below are our answers to your questions.

Q1: In the manuscript entitled “Alternative Liquid Assisted-Sintering of Al/Cu composites using selective powders of as-cast Al-Zn alloy”, the author demonstrated a way of synthesizing noncommercial Al6Cu5Zn alloy by PM. There exist a lot of uncertainties, which need to be substantially revised. Detailed comments are made below: The author said that “Cu powder particles are easily identified since their particles are brighter than other particles due to the SEM technique used (secondary electron technique) and higher molecular weight.” Since the secondary electron is not sensitive to the atomic mass, this narrative may not be right. Please provide a more convincing reason for this phenomenon.

AUTHORS: The Reviewer is correct. Authors are apologized for this mistake. The sentence was revised and correct term used. This modification is yellow highlighted.

Q2: The author mentioned that “the irregular sizes of powders facilitate the rearrangement between particles, and consequently, the porosity after sintering is decreased.” Have the author compared their results with spherical particles?

AUTHORS: The Reviewer also is correct. This has been theoretically and experimentally reported, as these references. Concern to comparison with spherical particles, we have not carried out this. We are apologized with this no experimental stage.

[A] J.B. Fogagnolo, F. Velasco, M.H. Robert, J.M. Torralba. Effect of mechanical alloying on the morphology, microstructure and properties of aluminium matrix composite powders. Mater. Sci. Eng. A, 342 (2003) 131-143.

[B] J.B. Fogagnolo, M.H. Robert, J.M. Torralba. Mechanically alloyed AlN particle- reinforced Al-6061 matrix composites: Powder processing, consolidation and mechanical strength
and hardness of the as-extruded materials. Mater. Sci. Eng. A, 426 (2006) 85-94.

[C] H.R. Hafizpour, A. Simchi, S. Parvizi. Analysis of the compaction behavior of Ale SiC nanocomposites using linear and non-linear compaction equations. Adv. Powder Technol., 21 (2010) 273-278.

Q3: What is “The energy to activate the diffusion mechanisms is also increased”? Which kind of energy does it refer to? It is true that diffusion is related to temperature, but there does not exist the activation energy.

AUTHORS: The Reviewer also is correct. In order to elucidate this matter, the sentence concerning to, was revised and improved. Modifications are yellow highlighted: …with increasing temperature, and the diffusion is increased.

Q4: Please label different phases in the SEM images. It seems there are several phases in the alloys.

AUTHORS: We congratulate this Reviewer’s comment. Some new sentences were included in order to elucidate this matter. Also, the figure caption was revised and improved.

Q5: And also, why does the alloy sintered at higher temperatures look less uniform than the low temperature sintered alloy?

AUTHORS: We congratulate this Reviewer’s observation and we are apologizing. The Fig. 4 is been corrected in order tor clearly depicts all phases constituted.

Q6: Because the alloy is brittle, the justification for the comparison of their strength is insufficient. All the samples break before yielding! Hardness data is more useful for the purpose.

AUTHORS: The Reviewer’s comment is pertinent, but Authors have decided to demonstrate both hardness and UTS results since at both industrial practices and scientific/technological fields these parameters are very important and utilized to planning cycle-life time of structures and components. Additionally, the comment corroborates with the fact that no yield strengths of the examined alloys are determined and mentioned.

Q7: If the author sinters the alloy for a longer time, it is possible to make a fully dense alloy?

AUTHORS: No, it is not possible. This is associated with intrinsic defect of manufacturing process (route), which differs reasonably from the theoretical assertions or theoretical density of material.

Q8: The author mentioned that “atomic diffusion of Cu is intense”. Technically, it is right. But some calculations on the diffusion distance are needed.

AUTHORS: The Reviewer also is correct. No calculations are provided. Firstly, due to this is not the focus of the present investigation. Secondly, the proposed sentence was only written in order to clarify or to mention to future readers that diffusion is predominant and facilities the intermetallic/thermodynamic condition be constituted. In this sense, in order to prevent some uncertain into the sentence, the follow sentence was deleted: “At this sintering temperature, it is recognized that diffusion of Cu into Al is higher than 10^-8 cm².s^-1 [22, 23]. This promotes thermodynamic conditions for the formation of the Al₂Cu intermetallic phase.”

Round 2

Reviewer 1 Report

 Accept in present form

Reviewer 3 Report

Basically, the author has made satisfactory revisions and clarifications to the manuscript, which I think is sufficient to address my concerns.

BTW, I may suggest that the author could provide a detailed reference about the revisions in the future, such as “On page xxx line xxx, we have revised xxx as xxx”, instead of just saying “modifications are yellow highlighted”, which can facilitate the review process.