Microstructure and Mechanical Properties at Elevated Temperature of Powder Metallurgy Al-Zn-Mg-Cu Alloy Subjected to Hot Extrusion

Round 1

Reviewer 1 Report

The manuscript  “Microstructure and mechanical properties at elevated temperature of powder metallurgy Al-Zn-Mg-Cu alloy subjected to hot extrusion” is dedicated to investigating microstructure and mechanical properties at elevated temperature Al-Zn-Mg-Cu powders containing 0.15 wt.% and 0.33 wt.% oxygen. Below are questions and comments to authors:

1.“For improving the high-temperature strength of Al–Zn–Cu–Mg alloy, a suitable microstructure is required, which may consist of thermally stable and coarsening resistant dispersoids [14], for instance, adding Zr and Sc to Al-Zn-Mg-Cu alloy to form thermal stable Al3 (Zr, Sc) dispersed in the matrix can improve its room temperature and high temperature performance [15-18]”  It is not clear how does this information relate to the current research. Do the authors use the Sc and Zr to provide the dispersoids? 
2. It is not clear how the authors confirmed the amount of oxygen in the powder.
3.“The hot extrusion was carried out at 420 ℃” Could the authors justify the use of this temperature based on previous literature data. 
4.“Then solution treatment and aging treatment were carried out at 120 °C/24 h and 470 ℃/2 h.” I think the solution treatment was at 470C and aging was at 120C. If SST temperature was 470C, why not carry out the extrusion at the same temperature to combine the operations?
5.The error bars are required for theYS/UTS/El values in table 1.

6.The manuscript is not designed according to the template of the Metals journal.

Author Response

Please see the attachment. 

Author Response File: Author Response.pdf

Reviewer 2 Report

The abstract is good

The introduction is little bit unstructured as in the first paragraph the authors should shows the benefits of material/process used and the challenge that actual community face!

The in the second paragraph they have to indicate what other researcher made to resolve and what was their weakness …

Also please clearly delimited your contribution to what other have made

And please indicate clearly which is the scientific novelty of this work

Please check the entire paper for different typos, here is just an example “0.05mm/s,” a space between value

Please provide details about sample preparation SEM/EBSD/TEM cause now they are missed and difficult to replicate it

How many samples were prepared for each type of trial ?

You have indicated “It shows that more Al2O3 is formed after the ball milling and oxygenation process” but now here I can distinguish this info ! at least from EBSD – normally it can be endorsed by some EDS analysis!

Figure 3 which is suppose to shows the dislocation tangle is very fuzzy and actually difficult to identify such kind of details ! better a zoom  but which should be a clear one !

Figures 4 (a), (b) and (c) shows the OIM – actually its shows EBSD micrographs !

Form Figure 5 d, e, f is almost no change in the texture  please double check

The results are interesting but their interpretation and discussion against literature data is very limited

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 3 Report

On the whole, the work is devoted to an important topic. But to make it more interesting for the reader, in my opinion, a number of revisions should be made.

1. It is necessary to expand the review part. The review is very brief and focuses mainly on very general issues. Only a couple of references are given specifically on the area of the study. It is necessary to provide the results of studies on the influence of oxygen on the structure and properties of the Al–Zn–Cu–Mg alloys system. The study implies that there are few such studies, but nevertheless they exist and some results have been obtained in them. Also in the review, it is necessary to answer the question, why do we need data on strength characteristics of the Al–Zn–Cu-Mg alloys system at elevated temperatures. Where will such data be used?
2. The section "Methods and materials" should be significantly expanded. It is necessary to write in detail about how the powders were mixed? Owing to what the oxygen content was changed? What equipment was used for mixing and in what modes did it work? What samples were taken for testing (dimensions)? According to what standards were mechanical tests carried out? On the whole, it is worth working out this section in detail, carefully describing the performed tests and describing them in as much detail as possible. It is necessary to write why namely such chemical composition was chosen for the study, and not another? It would be more obvious to present the chemical composition used to study the materials in the form of a table.
3. At the beginning of section 3, there is a reference to the experimental works that have already been carried out, both by their own and third party authors. This part could rightly be transferred to the first review section.

Between figures 5 and 6 there is a description of the transformations, proceeding in the samples during heating, and a description of the phases, presented in the figures. The presence of certain phases is usually confirmed by the phase analysis. Why in this case there are no such results? After all, the Al-Zn-Mg-Cu system is quite complex and the addition of oxygen can result in a sufficiently large number of compounds that will affect the properties of the samples.

4. For a better reader's perception, it would be good to expand the conclusions (1-3) a little bit. That is, it is necessary to add not only the obtained facts, but also a description of why it turns out this way.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors answered all the questions of the reviewer. The article was revised and designed according to the template of the journal. My decision to accept the article for publication in revised form.

Author Response

Thank you very much for you appreciation

Reviewer 2 Report

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Author Response

Thanks reviewer for good comments and hard work. We have significantly revised the English language

Reviewer 3 Report

Thanks to the authors for the significant work on the article. It is much better now.

However, some more corrections can be made.

About the answer to Point 4 from the first review: You have answered the question, it would be good to add your answer to the text of the article so that the readers understand immediately why there is no detailed phase analysis.

In Figure 7, it would be good for perception to slightly increase the graphs. Figure 7 contains quite a lot of information and it would be easier to perceive it if Figure 7 were a little larger.

Author Response

Thanks reviewer for good comments and hard work. Please see the attachment.

Author Response File: Author Response.pdf