Processing and Mechanical Properties of Ti2AlC MAX Phase Reinforced AE44 Magnesium Composite
Round 1
Reviewer 1 Report
The manuscript "Processing and mechanical properties of Ti2AlC MAX phase reinforced AE44 magnesium composite" has been reviewed.
As the title suggests, this is descriptive. No hypothesis is stated. No question to be answered by this research is phrased. An unclear number of experiments are conducted under unclear conditions. Some of the obtained results are analyzed with standard methods, described and compared to some data of unclear origin. If any new understanding, new methods or new ideas are presented, or how this manuscript presents foundations to build upon in the future, remains unclear. Quality of presentation in text, graphics and language is quite high. Statements regarding conflicting interests and authors' contributions are lacking entirely.
Therefore, major revision is suggested.
Open questions, preferrably to be answered in revised manuscript:
- since motivation is light-weight design, what is actually the mass density of the compound compared to AE44 or other relevant Mg alloys?
- what porosities were found in samples?
- how could statements about Young's modulus or stiffness be made?
- what are the reasons for the observed agglomeration of Ti2AlC? how could Ti2AlC potentially be distributed more homogeneously in future?
- which of the statements in section "4 Summary" are actually new knowledge presented in this manuscript for the first time? Please differentiate more clearly from the authors' previous publications and from publications of others.
- what is the meaning of the new knowledge? Is the investigated material and process route a good candidate for future lightweight application? How could it be improved further?
- please give an outlook for future research and how it can benefit from this
1 intro
The intro appears to be too broad and too little specific to this particular manuscript.
The mission statement of the manuscript appears to be "It was reported that AE44 alloy has better wear resistance and mechanical properties than AZ91D alloy at high temperature [3, 4]. Herein, we fabricated Ti2AlC reinforced AE44 composite and investigated the mechanical properties with different Ti2AlC orientations introduced by hot extrusion procedure"
If high temperature behaviour is of interest, why were only tests at room temperature conducted?
If wear resistance is of interest, why was it not tested?
2 Methods
How many mechanical samples were oriented parallel and orthogonal to extrusion direction? Please state unmistakably in this section as well as in each figure and table with results.
How was MAX phase and AE44 brought together in stir casting? This is essential to interprete the experiments and must be made clear to the reader of the manuscript without having to check referenced publications.
Why was 15 vol% of Ti2AlC chosen?3 Results & Discussion
Fig 3: please add to the images, which ones show as cast, parallel and orthogonal to ED, same way as in Fig. 1 which is very good. Also please graphically indicate delamination zones in as cast.
Equation 1: Please explicitly state in text, if delta is degree of potency or something else.
Table 1: please add number of tested samples
Fig. 6 - why is only a single curve shown for each condition and not all the test results? How was determined which data is shown and which were discarded? Or was only one test conducted for each material condition?
Why is "extruded AE44" appearing here out of nowhere? This material condition has never been mentioned before in the whole of the manuscript. Why not use "as cast AE44" used for comparison, as before?
Any interpretation of these diagrams in Fig.6 is highly questionable. Please plot curves of all tested samples to avoid any suspicions of bias. If reference data is necessary that was not obtained from the experiments described in this manuscript, please clearly highlight in the figures, properly reference the sources and explain the reasons for necessity in the main text.
Please add stress-strain curves of all conducted tensile tests and discuss.
Author Response
Please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
What is the chemical composition of the alloy used in this study? P2L80- is reference 33 about Authors previous study? Why did Authors use 15 % of reinforcement phase?
Author Response
Thank you for your question and the information was given in the revised manuscriupt.
The chemical composition is comercial AE44. Al( 3.6~4.4), ( RE (3.6~4.6) and Mn (0.18~0.50) in weight percent.
The reference is about our previous study.
In the application of cylinder bores, the reinforcement volume in composite is generally 15%.( Interfacial and fracture behavior of short-fibers reinforced AE44 based magnesium matrix composites,Journal of Alloys and Compounds 504 (2010) 527-534)
Reviewer 3 Report
The authors presented an interesting experimental research on processing and mechanical properties of Ti2AlC MAX phase reinforced AE44 magnesium composite. However, there are still some minor comments need to be addressed.
1- In page 2/11 in the last paragraph of introduction, “…happened in Ti2AlC composite at relative high load and speed.” It seems repetiting of “at relative high load and speed” so it should be better to remove this part. However it is recommended to re-write the all of the last paragraph to show the clear research objective.
2- In the page 3/11 Mechanical properties, what was the strain rates used during tensile and compression tests? Please include this information in your experimental methode. Additionally, there is only compression test results not tensile test in the manuscript. If you do not include it please remove tensile test from the above statement.
3- In the page 3/11 end of the first paragraph of Results and discussion, it is recommended to add more discussion using recent references to show the effect of hot extrusion as follows;
“This strong effect of hot extrusion to make homogenious distribution and refinement of reinforced particles has been reported in other metal matrix composites [ref].
[ref] Synergistic strengthening mechanisms of copper matrix composites with TiO2 nanoparticles.
4- In page 4/11, the authors claimed that basal plane of composite and reinforced particles could be parallel to the extrusion direction. But based on the XRD results in Fig. 2 peaks intensity of 001 plane of composite in ⊥ED was much larger than llED. This means, basal plane is perpendicular to the extrusion direction not paralell! In addition, could you identify the peak emitted from the basal plane of Ti2AlC?
5-In page 5/11 , Can authors show How did you calculate the interfacial shear strength between Ti2AlC and Mg? (250-350MPa)
6- There are some typo errors in page 6/11; Fig 3 dedonding should be debonding and Bramfitt should be correct.
7- In page 8/11; normally strain hardening rate is calculated based on TRUE S-S curve. So it would be better to show the True strain and Nominal strain in the S-S curves ploted in Fig 6. Adiitionally, in the last paragraph, “…resulted in one higher strain hardening rate.” What do you mean by “one higher”?
Author Response
Please see the attachment
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have made improvements in the revised manuscript and some explanations in the cover letter.
However, the main issue persists: There appears to be no scientifically relevant new insight presented. Experimental results are presented and described.
Furthermore, the experimental data is not presented completely. In the manuscript, it is not explained, how the choice was made which results to present and which to keep hidden. If it were indeed for better presentation and visibility, as stated in the cover letter, the rest of the results should have been presented in the appendix, with all diagrams and with key values of each experiment in a table.
The third major issue is that mandatory sections "author contributions" and "conflicting interests" are still missing.
All three main issues were addressed by this reviewer in the first review. None have been solved in the revised manuscript.
In conclusion, this reviewer suggest to reject this manuscript.
Details for consideration by the authors with regard to future manuscripts:
If there is indeed new understanding that was not there before this manuscript, it must be pointed out clearly, what it is. It must be differentiated from the situation in published literature before this manuscript.
Or is this only about gathering experimental data? Gathering Data is worthwhile, but it is not science. Therefore it should not be published as an original research article in a scientific journal such as MDPI materials. Questions that may guide the authors: Has similar material been analyzed in similar ways before? Are the test results surprising in any way or were they to be expected based on previously existing knowledge? Are they good, insufficient or irrelevant for the intended application? What expectations can be drawn for elevated temperature and wear behavior?
The situation of a larger funded project that is described in the cover letter may be of crucial importance to the authors. However, it is irrelevant to the scientific community.
If it is the case that scientific discussion and conclusion can only be made after future steps of experimental research will have been completed, it might be a better idea to publish a paper that includes these future results together with meaningful discussison and conclusion.
Mandatory sections "author contributions" and "conflicting interests" are still missing, although requested explicitly by this reviewer:
cited from the template https://www.mdpi.com/files/word-templates/materials-template.dot
lines 97-103:
Author Contributions:
For research articles with several authors, a short paragraph specifying their individual contributions must be provided. The following statements should be used “Conceptualization, X.X. and Y.Y.; methodology, X.X.; software, X.X.; validation, X.X., Y.Y. and Z.Z.; formal analysis, X.X.; investigation, X.X.; resources, X.X.; data curation, X.X.; writing—original draft preparation, X.X.; writing—review and editing, X.X.; visualization, X.X.; supervision, X.X.; project administration, X.X.; funding acquisition, Y.Y. All authors have read and agreed to the published version of the manuscript.”, please turn to the CRediT taxonomy for the term explanation. Authorship must be limited to those who have contributed substantially to the work reported.
lines 111-117
Conflicts of Interest:
Declare conflicts of interest or state “The authors declare no conflict of interest.” Authors must identify and declare any personal circumstances or interest that may be perceived as inappropriately influencing the representation or interpretation of reported research results. Any role of the funders in the design of the study; in the collection, analyses or interpretation of data; in the writing of the manuscript, or in the decision to publish the results must be declared in this section. If there is no role, please state “The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results”.
Only mentioned in the cover letter, but not in the manuscript: What important open questions are to be investigated in future research?
For the choice of 15% reinforcement, at least a reference should be given if no scientific reason can be given. Currently, it is simply stated that 15% is the way to go.
No statement on the porosity or the relative density in percent is made in the manuscript, only in the cover letter.
Opposed to the statement in the cover letter, the number of experiments has not been added to the results in fig. 6, table 1 and fig 3 a). This is essential for any reader to grasp the strength of any conclusions.
All tensile and compressive diagrams should have been added as an appendix, if the authors prefer not to combine them in a single diagram for better visibility. All the key data of each experiment such as UTS, TYS, elongation and UCS should have been put in a table. This table may have been moved to appendix, as the authors would see fit. Results cannot be simply omitted without disclosing how the choice was made, which results are presented.
Citation from https://www.mdpi.com/journal/materials/instructions#referees:
"Materials does not publish pilot studies or studies with inadequate statistical power."
Author Response
Please see the attachment
Author Response File: Author Response.pdf
