Mechanical and Tribological Behavior of Gravity and Squeeze Cast Novel Al-Si Alloy

Round 1

Reviewer 1 Report

REVIEW

on article

Mechanical and tribological behavior of gravity and squeeze cast novel Al-Si alloy

Vadlamudi Srinivasa Chandra, Koorella S.V.B.R. Krishna, Manickam Ravi, Katakam Sivaprasad, Subramaniam Dhanasekaran and Konda Gokuldoss Prashanth

SUMMARY

The article is written on a relevant topic and is of interest. The study aimed to investigate the effect of the applied compression pressure on the microstructure during solidification of the Al-Si-Cu-Fe alloy and their effect on the mechanical and wear-resistant behavior of the alloy.

The article has novelty and practical significance. The study makes it possible to determine the high-temperature wear resistance of the new Al-Si HPSC alloy, making it suitable for critical industrial applications.

At the same time, the article also has disadvantages. Therefore, it is necessary to correct the notes below.

COMMENTS

1. The Abstract should contain the prerequisites and the purpose of the research, a brief description of the methods used, the generalization of the article's main conclusions, and their interpretation. In this regard, the authors need to add the background and purpose of the study. In addition, the expressions "superior mechanical properties", "enhanced wear resistance", "the reduced coefficient of friction" should be supplied with quantitative results.
2. The authors used the minimum possible number of keywords. It is recommended to add 2-3 keywords to expand the terminology of searching for work on the Internet.
3. In the "Introduction" section, attention is drawn to rather large paragraphs that are difficult to read. In addition, the Introduction is too short, and many of the results of previous research have been considered in a superficial manner. The Introduction section needs to be expanded with a deeper analysis of previous works.
4. Aluminum, oxidizing, behaves like an abrasive material and therefore is not used in friction pairs. It is unclear in what devices the authors are going to use Al-Si alloys as wear-resistant materials. Give examples, please.
5. Why did the authors choose only wear resistance and tensile strength out of all the variety of mechanical properties?
6. It is known that aluminum alloys perform poorly under cyclic and shock loading conditions. The authors ignore these properties.
7. Also, the main aim of the study should be highlighted in a separate paragraph. There is a lack of transition between the literature review and the formulation of the research goal, for example, highlighting the differences between previous research and this research. In this regard, it would be necessary to clearly highlight in the Introduction section the relevance and scientific novelty of the research and break the text of the section into smaller semantic paragraphs.
8. In Section 2 "Experimental Procedure", add the manufacturer's name, city and country for each measuring instrument used in the study and each piece of test equipment. It is also necessary to make references to the standards used and add them to the "References" section.
9. Line 112 lists three different applied loads of 20 N, 40 N and 60 N, while Table 2 only lists 20 N and 60 N. This difference needs to be clarified or corrected in the text.
10. The methods should be described in as much detail as possible. Therefore a description of the operating principle of the wear test device should be added (Figure 1).
11. In the section "Results and discussion" in line 128 when describing photographs of the microstructure obtained during the study, a reference to the source is given [38]. It is not entirely clear what the link is for in this paragraph. I need to clarify.
12. A more detailed description of microstructure photographs is lacking, in particular, Figures 2b, 2c, 2d, 2e and 2f. In addition, there are no references in the text to these parts of Figure 2.
13. More than 20% of the References are the work of the study's authors. These References are mainly provided in the description and discussion of the results obtained. Self-citation is too high, and clarification is needed, for what purposes References are provided in this section. Is this a continuation of previous studies or a comparison with the results of previous studies?
14. Similarly, as for Figure 2, it is necessary to add links in the text and a short description of Figure 5, or rather its parts 5a and 5b and Figure 6 (a1, a2, b1, b2, c1, c2). A more detailed comparison of the given micrographs with references to them is necessary.
15. The article lacks a detailed comparison of the results obtained by the authors with similar works by other scientists. The "Results and Discussion" section mainly contains links to other works of one of the authors of this study. Therefore, the authors are encouraged to add at the end of Section 3 "Results and Discussion" a detailed comparison with the results obtained by other researchers (2-3 paragraphs). Or highlight the discussion in a separate Discussion section.
16. Section 3 "Results and discussion" is followed by section 5 "Conclusions". It is necessary to correct the numbering of the sections.
17. In the "Conclusions" section, there is no quantification of the research results. Must be added.

Author Response

Reviewer 1

The article is written on a relevant topic and is of interest. The study aimed to investigate the effect of the applied compression pressure on the microstructure during solidification of the Al-Si-Cu-Fe alloy and their effect on the mechanical and wear-resistant behavior of the alloy. The article has novelty and practical significance. The study makes it possible to determine the high-temperature wear resistance of the new Al-Si HPSC alloy, making it suitable for critical industrial applications. At the same time, the article also has disadvantages. Therefore, it is necessary to correct the notes below.

Thanks for the review and for the positive and constructive criticism. We have extensively modified the manuscript based on your comments and the modifications are suitably highlighted.

The Abstract should contain the prerequisites and the purpose of the research, a brief description of the methods used, the generalization of the article's main conclusions, and their interpretation. In this regard, the authors need to add the background and purpose of the study. In addition, the expressions "superior mechanical properties", "enhanced wear resistance", "the reduced coefficient of friction" should be supplied with quantitative results.

As suggested, the purpose of the research has been explained and quantitative results are included in the abstract. Accordingly, the following sentences have been included.

Automotive industry traditionally reduces weight primarily by value engineering and thickness optimization and both these strategies have reached their limits. A 6% reduction in automotive truck mass results in a 13% improvement in freight. Aluminum alloys have lower weight, relatively high specific strength, and good corrosion resistance and the present manuscript involves manufacturing Al-based alloy by squeeze casting.

Results demonstrated that squeeze casting of the novel Al-Si alloy at high-pressure exhibits a 47% increase in tensile strength, 33% increase in hardness, 10% reduction in coefficient of friction, and 15% reduction in wear loss compared to the GDC counterpart.

The authors used the minimum possible number of keywords. It is recommended to add 2-3 keywords to expand the terminology of searching for work on the Internet.

Thanks for the suggestion. As suggested by the reviewer, we have included additional references: Microstructure, Mechanical properties, Pin on Disc wear testing.

In the "Introduction" section, attention is drawn to rather large paragraphs that are difficult to read. In addition, the Introduction is too short, and many of the results of previous research have been considered in a superficial manner. The Introduction section needs to be expanded with a deeper analysis of previous works.

We agree with the reviewer's comments and as suggested we have modified the Introduction.

Aluminum, oxidizing, behaves like an abrasive material and therefore is not used in friction pairs. It is unclear in what devices the authors are going to use Al-Si alloys as wear-resistant materials. Give examples, please.

The present study aims at developing commercial vehicle components like spring brackets, fifth wheel coupling, etc. where both strength and wear resistance are required.

Why did the authors choose only wear resistance and tensile strength out of all the variety of mechanical properties?

The automobile components like spring brackets and fifth wheel couplings where Al-Si finds its application require adequate strength and wear resistance and hence only these properties are given importance in the present study.

It is known that aluminum alloys perform poorly under cyclic and shock loading conditions. The authors ignore these properties.

Cyclic and shock-loading conditions are not experienced continuously by these alloys in the application conditions like spring brackets and fifth wheel couplings. Hence, only the requisite properties are tested and not properties under cyclic and shock-loading conditions.

Also, the main aim of the study should be highlighted in a separate paragraph. There is a lack of transition between the literature review and the formulation of the research goal, for example, highlighting the differences between previous research and this research. In this regard, it would be necessary to clearly highlight in the Introduction section the relevance and scientific novelty of the research and break the text of the section into smaller semantic paragraphs.

As suggested by the reviewer, the Introduction section has been modified and the aim of the present study is suitably highlighted.

In Section 2 "Experimental Procedure", add the manufacturer's name, city and country for each measuring instrument used in the study and each piece of test equipment. It is also necessary to make references to the standards used and add them to the "References" section.

As suggested by the reviewer, the manufacturer’s name, city, and country for each measuring instrument have been introduced. In addition, the references for standards have been added.

Line 112 lists three different applied loads of 20 N, 40 N and 60 N, while Table 2 only lists 20 N and 60 N. This difference needs to be clarified or corrected in the text.

Sorry for the confusion. The content in Table 2 has been modified so that all three loads are included.

The methods should be described in as much detail as possible. Therefore a description of the operating principle of the wear test device should be added (Figure 1).

Thanks for the comment. As recommended, the description of the operating principle of the wear test device is added in the experimental section. The addition includes:

The wear testing machine consists of a specimen in the form of a pin and it is tested against a disc made of EN31 material according to the ASTM G99-05 standards. In addition, the load is applied through the loading panel, and the entire equipment is operated using a computer-based controller. All the parameters including depth, force, temperature, speed of the disc, time, etc. can be controlled using the controller in an acute fashion.

In the section "Results and discussion" in line 128 when describing photographs of the microstructure obtained during the study, a reference to the source is given [38]. It is not entirely clear what the link is for in this paragraph. I need to clarify.

The cited reference also shows the variation of grain size w.r.t pressure, which is in line with the present manuscript and hence cited accordingly.

A more detailed description of microstructure photographs is lacking, in particular, Figures 2b, 2c, 2d, 2e and 2f. In addition, there are no references in the text to these parts of Figure 2.

As suggested by the reviewer, Fig. 2(b-f) is explained and necessary references are added. The inclusions are:

…‘using optical (Figure 2(a-c)) and scanning electron microscopy (Figure 2(d-f))’….‘The microstructure gets refined with the application of pressure.’…..‘Similar observations were made by Amar et al. [40], where 2017A alloy was squeeze cast using GDC and at high pressures. Moreover, Amar et al. has shown that with the application of pressure, a refined and homogeneous microstructure was observed, which is in agreement with the present results.’

More than 20% of the References are the work of the study's authors. These References are mainly provided in the description and discussion of the results obtained. Self-citation is too high, and clarification is needed, for what purposes References are provided in this section. Is this a continuation of previous studies or a comparison with the results of previous studies?

Firstly, we would like to clarify that the present work is not a continuation of any present study. Secondly, we would like to iterate that references that are related to the context of the present manuscript and mostly from recently published articles are cited (more than 40% of the references from the last four years).

Similarly, as for Figure 2, it is necessary to add links in the text and a short description of Figure 5, or rather its parts 5a and 5b and Figure 6 (a1, a2, b1, b2, c1, c2). A more detailed comparison of the given micrographs with references to them is necessary.

As suggested by the reviewer necessary descriptions were included for Fig. 5 and Fig. 6.

The article lacks a detailed comparison of the results obtained by the authors with similar works by other scientists. The "Results and Discussion" section mainly contains links to other works of one of the authors of this study. Therefore, the authors are encouraged to add at the end of Section 3 "Results and Discussion" a detailed comparison with the results obtained by other researchers (2-3 paragraphs). Or highlight the discussion in a separate Discussion section.

We have introduced and compared the present results with existing results in the results and discussion when and where necessary as suggested be the reviewer.

Section 3 "Results and discussion" is followed by section 5 "Conclusions". It is necessary to correct the numbering of the sections.

Thanks for pointing out the error. We have modified it accordingly.

In the "Conclusions" section, there is no quantification of the research results. Must be added.

As suggested, quantification of the research results is included in the Conclusions part.

Reviewer 2 Report

The manuscript entitled “Mechanical and tribological behavior of gravity and squeeze cast novel Al-Si alloy ” has investigated the effect of applied pressure of squeeze cast and gravity cast on their microstructural evolution, mechanical and wear behavior. It presents some valuable results but compulsory revision is needed before it can be accepted. My comments are following.

1. Some writing errors remain to be corrected. For example, Section 2, Page 2, “high_pressure” and “de termined” should corrected to “high-pressure” and “determined”, respectively. section 3.4, page 5, “co-efficient” should be corrected to “coefficient”.
2. Section 3.2, page 4, “there is significant variation in hardness values as observed from the surface to core indicating the absence of porosity and other casting defects.” 1) Why significant variation in hardness indicates the absence of defects？This conclusion may be contrary the my general understanding. 2) More evidences, such as SEM images, are required to prove the conclusion that defect cause the variation of hardness.
3. Please use the full name or abbreviation uniformly, such as “Figure” or “Fig.”.
4. Section 3.5, page 7, 1) the word “Fracture analysis” is not accurate to describe the worn morphologies. 2) “delamination and micro-cracking may be observed in the samples produced through the GDC route”, Please point out or show clearly the delamination and micro-cracking in corresponding images.
5. The latest papers regarding wear behavior and hardness testing are suggested for discussion: ACS Appl. Mater. Interfaces 2021, 13, 55712−55725; Int. J. Plast. 142 (2021) 102997. 

Author Response

Reviewer 2

Some writing errors remain to be corrected. For example, Section 2, Page 2, “high_pressure” and “de termined” should corrected to “high-pressure” and “determined”, respectively. section 3.4, page 5, “co-efficient” should be corrected to “coefficient”.

Thanks for finding the error. We have rectified it accordingly.

Section 3.2, page 4, “there is significant variation in hardness values as observed from the surface to core indicating the absence of porosity and other casting defects.” 1) Why significant variation in hardness indicates the absence of defects？This conclusion may be contrary the my general understanding. 2) More evidences, such as SEM images, are required to prove the conclusion that defect cause the variation of hardness.

Casting generally leads to heterogeneous structures due to differences in the cooling rates observed from the edges to the core. Such differences in the cooling rate lead to differences in the microstructure and hence the variation in the hardness from surface to the core. The observed variation is found to be 22 % for the GDC sample and is reduced to 10% for the HPSC counterpart. It may be inferred from this that the squeeze pressure plays a significant role in microstructural homogenization. In general, increasing the pressure during solidification reduces porosity and it can be observed from several of the published reports. Hence, reduction in porosity also aids in increasing the mechanical behavior of the present samples produced in the HPSC condition as compared to the GDC counterpart.

Please use the full name or abbreviation uniformly, such as “Figure” or “Fig.”.

We have used Figure uniformly in the revised version of the manuscript.

Section 3.5, page 7, 1) the word “Fracture analysis” is not accurate to describe the worn morphologies. 2) “delamination and micro-cracking may be observed in the samples produced through the GDC route”, Please point out or show clearly the delamination and micro-cracking in corresponding images.

‘Fracture analysis’ is changed to ‘Surface analysis’ as suggested by the reviewer. Similarly, delamination and micro-cracking are marked directly in the Figure.

The latest papers regarding wear behavior and hardness testing are suggested for discussion: ACS Appl. Mater. Interfaces 2021, 13, 55712−55725; Int. J. Plast. 142 (2021) 102997.

The latest papers are used for discussion including the suggested articles.

Reviewer 3 Report

The article is devoted to the study of the microstructure, mechanical properties and wear characteristics of new alloys based on Al-Si. This research topic is one of the most relevant today, and the selected research objects have a high potential for practical application. In my opinion, this work deserves to be accepted for publication after the authors make corrections and additions that arose during its reading.
1 In the introduction, should authors elaborate on the relevance and purpose of the study, and the choice of test conditions?
2 Authors should indicate how they estimated the structural parameters, including grain size.
3 Was the size of defects and microcracks in the structure evaluated after wear tests?
4 Authors should indicate how the wear factor was determined?
5 Authors should provide comparative data with other experiments.

Author Response

Reviewer 3

In the introduction, should authors elaborate on the relevance and purpose of the study, and the choice of test conditions?

As suggested, the Introduction part is elaborated on the relevance and purpose of the study, and the choice of test conditions.

Authors should indicate how they estimated the structural parameters, including grain size.

We have not calculated any structural parameters nor included any grain size data in the manuscript and hence the query is not relevant to the context of the manuscript.

Was the size of defects and microcracks in the structure evaluated after wear tests?

Statistical evaluation of the size of the defects and microcracks was not carried out.

Authors should indicate how the wear factor was determined?

We have used the following articles to determine the wear factor – J. Mater. Res. 2016, 31, 55-65, and Mater. Lett. 2015, 142, 38-41. The above said articles have been cited where required.

Authors should provide comparative data with other experiments.

As recommended, comparative data/published literature were compared with the experiments as required in the revised version of the manuscript.

Round 2

Reviewer 1 Report

All my comments were taken into account and corrections were made in the text. I recommend the article for publication

Reviewer 2 Report

It's accepted now