MWCNT-Reinforced AA7075 Composites: Effect of Reinforcement Percentage on Mechanical Properties
Round 1
Reviewer 1 Report
The article is interesting and shows relevant results. However, to be accepted the authors need to carry out several corrections.
- The manuscript presents grammatical errors. It iis recommended that the authors review the writing of the article.
- Line 60 is not clear in the following text (0.-3% wt).
- Line 73 the authors must replace "0,5" to "0.5".
- Line 157 the letter K must be replaced by k corresponding to the equation 2.
- Figure 2 should include legend on the "y" axis.
- Line 200 the symbols [ ] not is clear.
- Figure 9 the peak related to MWCNTs is not clear. The authors should make an amplification of the graph in that area to show evidence of the presence of nanotubes.
- It is important to show the Raman results for both composites 0.5 and 1.
- The manuscript describes that the composites show high densification without the presence of pores. Authors must show evidence of the quantitative value of density in these composites.
- Show evidence of the distribution of the nanotubes in the metal matrix after the powder consolidation process.
Author Response
REVIEWER 1
Thank you for the time and effort that you have dedicated to providing feedback on our manuscript MWCNT-reinforced AA7075 composites: effect of reinforcement percentage on mechanical properties .We appreciate your insightful comments on revising the different aspects of the paper. We have incorporated most of the suggestions made. Those changes are highlighted within the manuscript.
Please see below, in blue, for a point-by-point response to your comments and concerns (We have also uploaded a document with our response in which you will see clearly the images included)
Comments and Suggestions for Authors
The article is interesting and shows relevant results. However, to be accepted the authors need to carry out several corrections.
- The manuscript presents grammatical errors. It iis recommended that the authors review the writing of the article. Thank you for your suggestion, the English writing has been revised throughout the manuscript.
- Line 60 is not clear in the following text (0.-3% wt). You are totally wright, we have corrected this error: (from 0 up to 3%wt)
- Line 73 the authors must replace "0,5" to "0.5". Corrected
- Line 157 the letter K must be replaced by k corresponding to the equation 2. Done
- Figure 2 should include legend on the "y" axis. Thank you for your advice, we have now included the legend on the axis.
- Line 200 the symbols [ ] not is clear. Yes, you are right; one reference was missing in between these brackets, now it is corrected.
- Figure 9 the peak related to MWCNTs is not clear. The authors should make an amplification of the graph in that area to show evidence of the presence of nanotubes.
This is a good observation; however, after considering the possible inclusion of a new insert in figure 9 with the enlargement of the region corresponding to the nanotube signal, we have finally decided not to do it, for the reasons explained below.
As you can see in the following image (please, see the uploaded document) it becomes evident that no peak is detected in either of the two concentrations of nanotubes studied in this paper. However, including this image as another part of Fig. 9, complicates its editing and makes it difficult to correctly visualize part a). On the other hand, as indicated in the text, the absence of this peak was already expected, because it is close to or below the detection limit of the technique and because of the effect that HEBM exerts on MWCNTs, as Esawi et al. explained in reference 35.
- It is important to show the Raman results for both composites 0.5 and 1. We agree that the Raman spectrum for composite 7075-0.5% MWCNTs could be included. However, we have decided not to do so for two reasons. First, because we consider that its inclusion does not provide any relevant detail regarding the aspects that are highlighted in this paper. Second, we are preparing a more in-depth work on characterizing the powders of the composite materials obtained under different milling conditions, and with different %wt MWCNTs, and we want to keep that composition and the corresponding discussion for future papers.
- The manuscript describes that the composites show high densification without the presence of pores. Authors must show evidence of the quantitative value of density in these composites.
After the extrusion process at 500ºC using a 7:1 extrusion ratio (ER) we have obtained fully dense profiles. In the microscopic examination performed by optical and electronic microscopy, we have not detected any porosity except for a small number of defects present at the ends (head and tail) of the profiles, which have been eliminated for performing the studies. Therefore, we have not made a quantitative determination of porosity. In the images that we show below, you can see the total absence of porosity.
- Show evidence of the distribution of the nanotubes in the metal matrix after the powder consolidation process.
When the distribution of the MWCNTs is homogeneous, it is not easy to demonstrate in the extruded profiles on microscopic level. However, we consider that the image in figure 13 allows us to verify that a homogeneous microstructure has been obtained after extrusion. In this composite material, agglomerates of CNTs are not seen and the intermetallic phase particles are regularly distributed.
To reinforce this idea, we present here (please, see the uploaded document) three LOM micrographs (1000x) for comparing the microstructure of the extruded profiles fabricated in the same conditions (high energy ball milling and hot extrusion at 500ºC) from: a) unreinforced 7075 powders; b) 7075-1% wt. MWCNTs and c) 7075-0.5% wt. MWCNTs. In all three cases, the same homogenous microstructure is achieved.
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a) Unreinforced 7075 powders (4h HEBM + 500ºC extrusion) |
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b) 7075-1%wt composite powders (4h HEBM + 500ºC extrusion) |
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c) 7075- 0.5%wt composite powders (4h HEBM + 500ºC extrusion) |
As a comparison, figure d) shows the microstructure of an profile extruder under the same conditions with powders of 7075-1% wt.MWCNTs. In this case, the composite powders were obtained using low-energy ball milling, in cycles of 200-300 rpm. In this case, insufficient dispersion of nanotubes is clearly observed.
On the other hand, at higher magnifications it can be seen that the MWCNTs are still partially entangled, as TEM micrographs in Figure 15 show.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This is a good original research paper on a new and potentially promising class of metal matrix composite (MMC), namely aluminium alloy 7075 reinforced with weight percentages of 0.5% and 1% multiwall carbon nanotubes. The authors have carefully characterised these composites using optical and scanning electron microscopy, X-ray diffraction and Raman spectroscopy. Table 3 shows a comparison of composite mechanical properties with Al 7075-O. While this is of scientific interest to show the effects of the reinforcement, 7075-O is not a useful engineering material. A more significant engineering comparison would be with 7075-T6. Taking literature values for 7075-T6 of Vickers hardness 175, YS=480 MPa, UTS=560 MPa, % elongation 5-11, the two composites have inferior properties to these. This comparison should be added to Table 3. Also, the % elongation of the 1wt% composite is very low at only 2. This implies it is essentially a brittle material, presumably with a very low fracture toughness. Fracture toughness or impact toughness tests should also have been performed on the composites. What is the cost of manufacturing the MMCs compared to the cost of producing Al 7075-T6? Can the composites be subsequently heat treated to the T6 condition after manufacture? This manuscript is let down by poor English and a lack of attention to detail. I have provided corrections to the worst examples below. However, the English needs to be further polished before publication.
Replace and als., et als. throughout the text with et al.
Page 1, Lines 9/10: …1% wt. and 0.5%... -> …1%wt and 0.5%wt…
Page 1, Line 18: …samples of of… -> …samples of…
Page 1, Line 20: Keywords: aluminum… -> Keywords: Aluminum…
Page 1, Line 34: …is especially… -> …are especially…
Page 1, Line 36: …during the… -> …during…
Page 1, Line 38: …pioneer work… -> …pioneering work…
Page 2, Line 43: But powder… -> However, powder…
Page 2, Line 44: …of composites. -> …of composite.
Page 2, Line 57: …affect the… -> …affects the…
Page 2, Line 59: …with the CNTs. -> …with CNTs.
Page 2, Line 71: …consisting in… -> …consisting of…
Page 3, Line 96: …oxidation. -> …oxidation, was used.
Page 3, Line 109: Should force of 40 Tm be force of 40 Ton?
Page 3, Line 124: What is measuring de diameter?
Page 3, Line 140: …compared the… -> …compared with the…
Page 4, Line 164: …in epoxi resin… -> …in epoxy resin…
Page 4, Line 164: …grinded down… -> …ground down…
Page 4, Line 170: …performed in samples… -> …performed on samples…
Page 4, Line 183: Caracterization… -> Characterization…
Page 5, Line 188: …small number satellites… -> …a small number of satellites…
Page 5, Line 200: Reference missing
Page 5, Line 205: …on this paper. -> …on in this paper.
Page 6, Line 224: That makes… -> That makes it…
Page 8, Line 284: …seams getting trapped… -> …seams get trapped…
Page 9, Line 306: …all that factors… -> …all those factors…
Page 9, Line 321: …the evolution of… -> …its evolution…
Page 9, Line 323: …previously referred… -> …previously referred to…
Page 10, Figure 10: This graph is confusing in terms of which curves are crystallite size and which are strain
Page 11, Line 349: …referred by… -> …referred to by…
Page 12, Line 392: …and the measured… -> …and those measured…
Page 12, Line 415: …quantified bay… -> …quantified by…
Page 12, Line 417: …of a 44%... -> …of 44%...
Page 13, Line 443: …formation severe… -> …formation of severe…
Page 13, Line 448: …specially… -> …especially…
Page 14, Line 475: Transversal section… -> Transverse section…
Page 14, Line 479 : …bay all… -> …throughout…
Page 15, Line 501: …the obtained… -> …that obtained…
Page 16, Line 512: This sentence does not make sense
Page 16, Line 528: …directions compared… -> …directions are compared…
Author Response
REVIEWER 2
Thank you for giving us the opportunity to submit a revised draft of our manuscript: MWCNT-reinforced AA7075 composites: effect of reinforcement percentage on mechanical properties
We appreciate the time and effort that you have dedicated to providing your valuable feedback on our manuscript. The authors have carefully considered the comments and tried our best to address every one of them. We hope the manuscript after careful revisions meet your high standards.
Please see below, in blue, for a point-by-point response to your comments and concerns.
Comments and Suggestions for Authors
This is a good original research paper on a new and potentially promising class of metal matrix composite (MMC), namely aluminium alloy 7075 reinforced with weight percentages of 0.5% and 1% multiwall carbon nanotubes. The authors have carefully characterised these composites using optical and scanning electron microscopy, X-ray diffraction and Raman spectroscopy.
We greatly appreciate the Reviewer’s positive comments.
Table 3 shows a comparison of composite mechanical properties with Al 7075-O. While this is of scientific interest to show the effects of the reinforcement, 7075-O is not a useful engineering material. A more significant engineering comparison would be with 7075-T6. Taking literature values for 7075-T6 of Vickers hardness 175, YS=480 MPa, UTS=560 MPa, % elongation 560, the two composites have inferior properties to these. This comparison should be added to Table 3.
Thank you for your valuable input in our manuscript. We have taken your suggestion by adding the comparison to 7075-T6 that is clearly more interesting for engineering purposes. We agree with the reviewer on this point. However it is not usual in published papers, as can be seen in the cited references, with which our results are compared.
Also, the % elongation of the 1wt% composite is very low at only 2. This implies it is essentially a brittle material, presumably with a very low fracture toughness. Fracture toughness or impact toughness tests should also have been performed on the composites.
You are right to indicate that it would be of great interest to carry out fracture toughness or impact toughness tests on composites, even though, in the bibliography consulted, its performance is not usual.
In this first work, we are interested in verifying if the proposed manufacturing method allows a correct dispersion of the nanotubes and its repercussion on the basic mechanical properties. Toughness tests are part of the experimentation we are currently developing.
What is the cost of manufacturing the MMCs compared to the cost of producing Al 7075-T6? Can the composites be subsequently heat treated to the T6 condition after manufacture?
We cannot hide that the final objective of our research as a whole would be to obtain a 7075 matrix composite reinforced with MWCNTs with characteristics superior to those of a conventional 7076 after T6 temper. For this, the first steps are the definition of the manufacturing parameters to achieve the correct dispersion of the nanotubes in the matrix, followed by the optimization of the extrusion. Simultaneously, the optimum proportion of reinforcement must be found to achieve the desired improvement in properties.
In the case of Al matrix composites reinforced with nanotubes, an increase in mechanical properties has been demonstrated with an increase in% of reinforcements up to a value from which they decrease. In the case of composites with 7075 matrix, there are no studies analysing this effect. In our work, it is shown that reducing the %wt MWCNTs there is an improvement in the mechanical characteristics, but we have not yet determined the optimal %wt to achieve the desired objective.
If this goal can be achieved, the T6 treatment would not be necessary and, therefore, there would be a significant decrease in the cost of the powder metallurgy route.
A second alternative would be, as you point out, performing a subsequent treatment of composites to the T6 condition. To our knowledge, this possibility has not yet been studied in 7075- MWCNTs composites, and it is an important part of our current research. Although our previous experience with other aluminium matrix composite materials suggests that HEBM makes the solubilisation step difficult and therefore limits subsequent precipitation hardening, the results cannot be extrapolated to this particular case.
This manuscript is let down by poor English and a lack of attention to detail. I have provided corrections to the worst examples below. However, the English needs to be further polished before publication.
We appreciate the Reviewer’s helpful comments, We regret there were problems with the English. The paper has been carefully revised to improve the grammar and readability.
Replace and als., et als. throughout the text with et al.
All the replacements have been done
Page 1, Lines 9/10: …1% wt. and 0.5%... -> …1%wt and 0.5%wt…OK
Page 1, Line 18: …samples of of… -> …samples of… OK
Page 1, Line 20: Keywords: aluminum… -> Keywords: Aluminum… OK
Page 1, Line 34: …is especially… -> …are especially… OK
Page 1, Line 36: …during the… -> …during… OK
Page 1, Line 38: …pioneer work… -> …pioneering work…OK
Page 2, Line 43: But powder… -> However, powder…OK
Page 2, Line 44: …of composites. -> …of composite. OK
Page 2, Line 57: …affect the… -> …affects the… OK
Page 2, Line 59: …with the CNTs. -> …with CNTs. OK
Page 2, Line 71: …consisting in… -> …consisting of… OK
Page 3, Line 96: …oxidation. -> …oxidation, was used. OK
Page 3, Line 109: Should force of 40 Tm be force of 40 Ton? OK
Page 3, Line 124: What is measuring de diameter? Oops, typing error: the diameter- corrected
Page 3, Line 140: …compared the… -> …compared with the… OK
Page 4, Line 164: …in epoxi resin… -> …in epoxy resin… OK
Page 4, Line 164: …grinded down… -> …ground down… OK
Page 4, Line 170: …performed in samples… -> …performed on samples OK
Page 4, Line 183: Caracterization… -> Characterization… OK
Page 5, Line 188: …small number satellites… -> …a small number of satellites… OK
Page 5, Line 200: Reference missing OK
Page 5, Line 205: …on this paper. -> …on in this paper. OK
Page 6, Line 224: That makes… -> That makes it… OK
Page 8, Line 284: …seams getting trapped… -> …seams get trapped… OK
Page 9, Line 306: …all that factors… -> …all those factors… OK
Page 9, Line 321: …the evolution of… -> …its evolution… OK
Page 9, Line 323: …previously referred… -> …previously referred to…
Page 10, Figure 10: This graph is confusing in terms of which curves are crystallite size and which are strain
Page 11, Line 349: …referred by… -> …referred to by… reported
Page 12, Line 392: …and the measured… -> …and those measured…OK
Page 12, Line 415: …quantified bay… -> …quantified by… OK
Page 12, Line 417: …of a 44%... -> …of 44%... OK
Page 13, Line 443: …formation severe… -> …formation of severe… OK
Page 13, Line 448: …specially… -> …especially…OK
Page 14, Line 475: Transversal section… -> Transverse section… OK
Page 14, Line 479 : …bay all… -> …throughout… OK
Page 15, Line 501: …the obtained… -> …that obtained… OK
Page 16, Line 512: This sentence does not make sense. We have rewritten it more clearly.
Page 16, Line 528: …directions compared… -> …directions are compared… OK
Author Response File: Author Response.pdf
Reviewer 3 Report
The article is prepared with extreme care. The publication presents current engineering issues. The paper deserves special recognition because of the subject matter presented, and in my opinion can be published in its present form.
The authors of this paper could only point out that the novelty of this paper in relation to other similar research papers should be better emphasized in the introduction section. Also, it would be reasonable to better refer in the conclusion section to the numerical data obtained during the research.
Author Response
REVIEWER 3
We thank you very much for your time spent carefully reviewing the manuscript, and we appreciate your favourable comments.
Comments and Suggestions for Authors
The article is prepared with extreme care. The publication presents current engineering issues. The paper deserves special recognition because of the subject matter presented, and in my opinion can be published in its present form.
Thank you very much for supporting the publication of our manuscript in its current form.
The authors of this paper could only point out that the novelty of this paper in relation to other similar research papers should be better emphasized in the introduction section.
Thank you for this suggestion. We have accordingly modified the paragraph in the revised manuscript, to emphasize the most innovative aspects of our work.
Also, it would be reasonable to better refer in the conclusion section to the numerical data obtained during the research.
Thank you for pointing this out. Even though we think that the main results are summarized in the conclusions, we have introduced some changes in this section to make clear our findings.
