Electron Microscopy Investigations of А356 Alloy Modified with Nanoparticles

Round 1

Reviewer 1 Report

The publication is of interest. Well written and concise.

 

Two spelling mistakes were found:

1) Line 90: postprocessed

2) Line 174: shows instead of shown

Author Response

The comments from reviewer #1 are typing errors. We thank the reviewer for the critical reading and for the positive comments. The corresponding changes are noted after each comment are colored in yellow. Additional critical reading of the manuscript was made and few misprints were corrected.

 

Two spelling mistakes were found:

1) Line 90: postprocessed - Response: “postprocesed” is changed to “postprocessed” (new line 100)

2) Line 174: shows instead of shown - Response: “shown” is changed to “shows” (new line 184)

Reviewer 2 Report

The paper is interesting, I do not have specific comment/suggestion.

Author Response

We thank the reviewer for the positive comment.

 

Reviewer 3 Report

 

This manuscript has little sense in its actual presentation. The origin of the samples, S1, S2, S3 y S5 is confused. The results are not clear, they are hardly commented,  the EBSD and LM images are nice, but the EDS analysis are strange and difficult to include.  As far as I am concern  it should be rethought and rewritten.

Author Response

We thank to the reviewer for this comment. It appears that we did not define in a clear way for the readers the cause and purpose of our study. We believe that the origin of the samples is not confused. In the casting practice, and in particular when the castings are modified with nanosized particles, different crystallization rates are possible in one casting. For this reason, we study the effect of nanoparticles on the structure of a complex casting (samples S1 and S2), which crystallizes at a relatively high rate (cast in metallic form). The other case (samples S3 and S5), considered by us, is the crystallization of a conical casting cooled by free air convection with a relatively low crystallization rate, characteristic for sand castings. In addition, we had the ability to precisely control the temperature during the crystallization process, and the chosen section is the region, where lies the thermocouple junction. The decrease in undercooling as a result of nanoparticles introduction is further evidence of the role of nanoparticles as crystallization nuclei. The results for the nanoparticles effect on the A356 microstructure indicate that in both cases investigated, we have a structure refinement, regardless of the different crystallization rates. The compared couples of samples (S1 - S2, and S3 - S5) were cut from the same castings section, melt and mould temperatures were the same, which is a guarantee that the observed microstructures and microhardness change is due only to nanoparticles addition.

In our previous investigations, references [44-49] in the paper, we were not able to find a single, or agglomerated nanoparticles. This is a hard task, keeping in mind on one hand the small quantities of added nanoparticles, and on the other hand – the small size of analyzed TEM foils.  The reason we did STEM analyses was to find the place of the nanoparticles in the solidified castings – are they close to the boundaries or inside the grains. This experiment helped us to conclude that observed grain refining is due to nanoparticles that act as nucleation sites during crystallization. Also in known references EBSD was not often used as method for analyses of grain refining, caused by nanoparticles addition, and we believe that our work could help other researchers to consider it and use it in their future investigations.

 

All the results are given in point 3. Results (page 4) while the comments/discussion is given in point 4. Discussion (page 9), according to journal “Metals” requirements. We believe the discussion and conclusions, based on the discussion, are well given and clear enough, however, we did our best to improve the discussion part and we added an additional information there.

 

Regarding the comment of the respected reviewer “…EDS analysis are strange and difficult to include…”  We appreciate very much this comment and added additional text and a table with the chemical composition of the base alloy (in wt%) were added in the Materials and methods and in the Discussion part. By doing this we hope that now socially this part of our paper is more clear and easy understandable.  

 

Additional texts regarding the above comments is added in the manuscript, colored in yellow:

Line 52-53: …., the composition of aluminum alloy (A356) is given in Table 1.

Line 56: Table 1 is inserted. The numbering of other Tables is corrected.

Line 57-64:  In the casting practice, and in particular when the castings are modified with nanosized particles, different crystallization rates are possible in one casting. For this reason, we study the effect of nanoparticles on the structure of a complex casting (Figure 1 -samples S1 and S2), which crystallizes at a relatively high rate (cast in metallic form). The other case (Figure 2 - samples S3 and S5), considered by us, is the crystallization of a conical casting cooled by free air convection with a relatively low crystallization rate, characteristic for sand castings. In addition, we had the ability to precisely control the temperature during the crystallization process, and the chosen section is the region, where lies the thermocouple junction.

Line 67: “for” is inserted

Line 79: “for” is inserted

Line 86-87: …. the casting …………., and the chosen section (shown with the white arrow in Figure 2) is the region, where the thermocouple is placed.

Line 94-103: “analysed” is corrected to “analyzed”

“curernt" is corrected to “current”

Line 125: (pixels) is added

Line 128-130: “The zones where the eutectic structures are formed are also clearly indexed and their grain size is also represented in the results, provided that they fulfil the above conditions” is removed.

Line 167-168: “In the above analyses the grain size of the eutectic structures is also taken into account.” is removed.

Line 184-191: ………………shows the …. the …………. of ………. - the unmodified (Fig. 3a) and the modified (Fig. 3b). ……………… (……… the …….. the ………… the ………. for the…..), it means that the cooling conditions that control the solidification process are identical. Hence, the ……… differences …………….. of the two samples …………………….. in the sample S2. As a concequence the ………………………. in comparisson to the sample S1, ………. correspondingly ……………. of the sample S2 ……………………………..

Line 210-226: Several specific points corresponding to the microstructure were analized. ………………………………………………………….. (see Table 1). This point is used as a kind of calibration point for the EDS measurement. …………………. measured ………………………………………………………………….. Such effects are common in the EDS/STEM analysis. Having in mind that the ………………………………, it is reasonable to ………………… specific …………….. for the nanoparticles, …………… increased .. content … the ……………………………………………………………………………………………………. The size of these conglomerates was around 130nm, wherease some individual nanoparticles with a size between 20nm  and 40nm can be disinguished inside the conglomerates (see Figure10). Similar ………………………………………………………………………………………………………………………………………………... Most ……………. the reason for the increased oxigen content is in ……………………………………………………………………………………………………………….

Line 232: ………………. samples, one ……………….. another ………………..

Line 235-238:                The ………. Cu-cladded …………… to the studied Al alloy ……… significantly the as-cast ……... After modification, the ………………………, and the ……………………………...  As a consequence of the grain refinement ……………. of the modified castings ……………………….

Line 239-242: ………., but not so effective ………………. in the Al castings …………………….. After modification with TiCN nanoparticles the ……………… diameter of the modified alloy ……………………….., and the ……………………., which resulted in an increase of ……………...

 

Following the issues, which were addressed in the reviewer comments, extra text was added, colored in yellow, in the manuscript. We believe it will help not only to reviewers, but also to scientific community to clarify and understand better our paper. Please find the attached revised manuscript.

Best regards,

R. Dimitrova

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

As far as I concern the manuscript is still improvable. The production route of the studied samples is unclear, as well as the terminology. Samples S1 un-modified and S2 modified from a complex casting, Fig. 1, without  any other explanation of how this piece was obtained ¡. Concerning samples S3 and S5 (sample S4 is missed) they are only described in the Figure captions of Fig. 2, simultaneously to the Thermal analysis test, really messy ¡¡.  I think that the authors should study deeper the results, they have used good and expensive techniques but the description of the results is short and consequently the conclusions are poor. With the addition of nano particles of SiC and TiCN I suppose an aluminium metal matrix composite is obtained, because are these NP dissolved in the Al matrix or they remain as a reinforcement ? ,  the manuscript is confused. The conclusion that the addition of particles refine the microstructure is obvious because it increases the surface for heterogeneous nucleation, and so on. Consequently in my opinion this work should be improved a lot, and I recommend to work it harder.  

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 3

Reviewer 3 Report

The authors have improved the manuscript