Microstructure and Tensile Properties of AlSi10Mg Alloy Manufactured by Multi-Laser Beam Selective Laser Melting (SLM)

Round 1

Reviewer 1 Report

 In the submitted document, the microstructure and tensile properties of both the multi-laser-formed AlSi10Mg isolated and overlap areas are studied. In this regard, the authors intend to ensure that the parts can achieve perfect seamless splicing and whether the parts in different regions have the same performance. Overall the document presents a good organization with a clear exposition of all issues in discussion.

Minor revisions

Line 113-114: “The microstructure of SLM-formed AlSi10Mg parts is superior to castings”. This sentence must be explored/described in another way. Microstructure … is superior..?

Figure 4. It is not understood why to present a well know phase diagram.

Line 223: “a-Al”, should be “alpha-Al”

Tensile properties: Why is it only presented the value of Tensile Strength? How many samples were tested (evaluated)? Standard deviation. Geometric characteristics of specimens tested?

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The paper concerns the study of the microstructure and tensile properties of multi-laser SLM of AlSiMg alloy. The topic is quite interesting in the field of additive manufacturing and with potential industrial significance. However, the manuscript needs drastic improvements in terms of language and terminology, as well as in the technical content to enhance readership and considered for publication in an international high quality Journal. More specifically:

Section 2. Materials and Methods.

1. A simple drawing could be considered helpful to understand the basic principles of the laser technique.

2. The process optimization should be reported in higher detail, based on the selection criteria. The units of the parameters need to be carefully addressed (exposure time).

3. Experimental methods paragraph demands higher accuracy in information regarding testing standard, specimen geometry, number of samples, testing rate, etc. This is basically referred to tensile testing technique.

 

Section 3. Results.

1. The micrographs mainly contained in Figure 3 and 5a-c, seem that they are of low contrast and resolution. Brightness needs also correction to depict the morphological features more clearly, while the colour is not necessary (greyscale could be a good choice for optical micrographs). Also, Figures 5a-c seem that they represent optical instead of SEM micrographs.

2. There are extensive text parts referred to textbook knowledge, such as the description of eutectic solidification using Al-Si equilibrium diagram (see Figure 4). This is also questionable concerning the rapid solidification (beyond equilibrium state) imposed by laser treatment. Also, the Ref. [5] for just the phase diagram seems rather irrelevant.

3. The solidification structures, depicted in Figures 5d-f and 7 is rather cellular than dendritic. Further information concerning e.g. microstructural details, inter-cellular areas, localized chemical composition, segregation phenomena, etc. is recommended to be included in the study.

4.The ratio G/R (not the product) represents the degree of constitutional undercooling (not the cooling rate).

5. The tensile testing findings need to be comprehensively approached and enhanced. Further results concerning tensile properties, such as stress-strain curves depicting also yield point and elongation are strongly suggested.

6. Fractographic analysis (Figure 8) needs also higher clarification and interpretation, concerning fracture mechanism occurrence. The first two micrographs (Figs 8a-b) seem that refer to the same magnification (x100). The two-scan fracture (Figs. 8c-d) does not look like as “smooth” brittle fracture (these micrographs also seem at the same magnification x5000). The sentence “the tensile properties… has decreased…” seems contradictory to the UTS values and fracture elongation, as it can be addressed by the SEM fractographic evaluation.

 

Section 4. Conclusions.

It is rather generic and brief. More accurate, conclusive results have to be included in this paragraph. Also, the correlation of tensile properties and fracture elongation/ductility needs a more clear and consistent assessment and interpretation.

 

References

Ref. [26] is remained from text template. It has to be removed.

 

Language/Terminology

The manuscript needs to be corrected in terms of grammar and technical/scientific language. There are various “odd” and “unusual” terms and expressions throughout the text which might distort the meaning and provoke misleading. Some examples are following:

 

“dendritic dendrites” (L. 177) “microstructure diagram” (L. 144) “near-alt eutectic phase” (L. 152) “are melted and integrated” (L. 172) “the catalytic cracking aluminium battery…” (L. 209) “replacement solid solution”, substitutional solid solution should be (L. 241) The word “tissue” in various places “building direction” (L. 255)

 

 

 

 

 

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

This paper explores the use of a multi-beam selective laser forming system to produce AlSiMg cast alloys. A qualitative evaluation of the microstructure development is provided. It is a shame that the authors haven’t attempted to provide a more quantitative analysis of their results. Please find some comments below.

The fact that the Mg2Si particles were not detected in XRD most likely comes from their relatively small volume fraction. Please give more details on the duration of acquisition of the XRD scans.

In the XRD analysis, it is said that the Al peaks are shifted to the right, this is nothing obvious from the figure, can a higher magnification on the main Al peak be provided? Also, it would probably be more accurate to say “shifted to higher angles” rather than “to the right”

The XRD analysis is very qualitative at this stage, would it be possible to provide fractions of Al versus Si and calculate the evolution of Si solute content in solid solution as a function of the number of scans?

Equation 3 is given but there is no calculations related to the reported results?

Figure 6, the label for the y-axis says “Indensity”

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Although the paper has been revised, there are still major issues that need to be addressed.

Especially in the section 3.2 and the relevant Conclusions section 4:

The stress-strain curves present slight differences among compared samples. Only tensile strength was reported (in Table 2) while there was a relevant argument for yield strength. Also, plastic (?) toughness is referred which is not quite proper and valid expression as fracture toughness was not determined. The strain to failure ranges within 1.5 and 2% approximately, which is not significant difference to support substantial variation in “ductility”. The low values of strain rather signify low ductility or almost brittle behaviour. The SEM fractographs (Figure 11) are not suitable to unfold the episodes of the fracture process and tell clearly the “fracture history”. Dimples were scarcely recognized, only some subtle indications of them (if existed). There are also other obscure areas, denoting deep cavities or flat facets (Figure 11c). Please check and advise. Also, in general, the type and morphology of fracture surface is result and not cause of tensile and fracture properties (“resulted from” instead of ”resulted in”, see L376-377). However, this claim cannot be substantially justified based on the present investigation findings. L353-355: seems contradictory; if internal pores increase then the ductility and elongation will be reduced. Please check and advise.

 

Other comments regarding the revised text:

Figure 7 includes rather low magnification SEM micrographs (7d, e). All the images’ details are barely seen, cellular structure, spot numbers, scale markers. Images need significant enlargement to be readable. EDS spectra elemental results need to be rounded to one decimal digit, as the most significant one. Elemental analyses in L251-252 is better to be placed in a Table. Please explain more thoroughly the difference in Mg, Si content between the spots and the nominal or general chemical composition, addressing also potential causes based on phase transportation and precipitation.

Grammar/Language

Although the grammar could have been improved, there are terms / expressions to be rechecked and revised for their technical soundness too:

L192: The crystals on the top plane are equiaxed crystal (pleonasm) L351: The microstructure becomes large (maybe coarse?) It referred in various places “Mg elements” (L249): The suggested expression is either Mg atoms or Mg element. Also in Table 2, the first row is named “Elements” (Property?)

Author Response

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Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

The paper has been revised and some additional revisions are suggested.

Scientific/Technical Comments

The elemental maps (Fig. 7) do not add any significant value; they seem very “flat” and the points are not distinguished and not any differentiation was observed.

L363-364: “is very shallow like a dimple” it is not understood and it seems meaningless.

Fracture surfaces seem quite similar (Fig. 11), as it was dictated also by the mechanical properties and σ-ε curves.

 

Spelling/Grammatical Comments

L253: “Si elements” is odd expression (Si atoms is better).

L335: Please keep one single space between numerical part and units of physical measurements.

L387: “SEM diagram” is not a suitable term: SEM micrograph or fractograph is much better.

L388: …becomes coarse.

 

 

 

Author Response

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Author Response File: Author Response.pdf