Oxide Behavior During Laser Surface Melting
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis manuscript systematically investigates the mechanisms of oxide formation during laser remelting, clearly identifying spatter oxidation and reworking of pre-existing oxide films as the main sources, while direct melt-pool oxidation plays a minor role. It provides important insights into the origin of oxide inclusions in LPBF components. After review, the following issues need to be addressed:
1.The conclusion that direct melt pool oxidation is negligible is based on oxygen mass transfer rate calculations. Are there additional experimental validations or literature references that corroborate this inference?
2.The manuscript states that reprocessing leads to the agglomeration of thin oxide films into larger oxide particles. Could the authors elaborate on the mechanisms by which such oxide agglomeration influences the distribution of microstructural defects during laser remelting? You may refer to Additive Manufacturing, 2025, 100:104685. to improve the description of defects and enhance the quality of the paper.
3. The study employs deep etching to analyze inclusions in IN718 but relies solely on surface observations for AlSi10Mg. Could this discrepancy in analytical methods lead to biased comparative conclusions?
4. The formation of oxide bands at the melt pool edges in AlSi10Mg varies with energy density (power/scan speed). Can the authors provide further validation or modeling to elucidate the mechanism by which heat input affects oxide band evolution?
5. A thorough proofreading of the manuscript is necessary prior to submission to ensure clarity and coherence.
Author Response
Comment 1: The conclusion that direct melt pool oxidation is negligible is based on oxygen mass transfer rate calculations. Are there additional experimental validations or literature references that corroborate this inference?
Response: We have added reference to the work of Chia et al., who considered direct oxidation, but only considered the region of the melt pool directly below the metal plume; we are not aware of other relevant work. Reference has also been added to related work that tested the effect of hatch spacing on the concentration of oxides. See references 24, 25 and 37, and lines 364-368 and 441-449.
Comment 2: The manuscript states that reprocessing leads to the agglomeration of thin oxide films into larger oxide particles. Could the authors elaborate on the mechanisms by which such oxide agglomeration influences the distribution of microstructural defects during laser remelting? You may refer to Additive Manufacturing, 2025, 100:104685. to improve the description of defects and enhance the quality of the paper.
Response: We have added a short discussion of the results reported by Smith (2022) (reference 37 in revised manuscript), who explicitly considered the relationship between the surface deposition and incorporation of oxides (lines 441-449).
Comment 3: The study employs deep etching to analyze inclusions in IN718 but relies solely on surface observations for AlSi10Mg. Could this discrepancy in analytical methods lead to biased comparative conclusions?
Response: The oxides on the surface of both IN718 and AlSi10Mg were studied in the same way, so these are comparable.
Comment 4: The formation of oxide bands at the melt pool edges in AlSi10Mg varies with energy density (power/scan speed). Can the authors provide further validation or modeling to elucidate the mechanism by which heat input affects oxide band evolution?
Response: Reference was added to work on laser polishing, noting the importance of Marangoni flow, and some additional discussion was added (lines 413-419).
Comment 5:
A thorough proofreading of the manuscript is necessary prior to submission to ensure clarity and coherence.
Response: Numerous corrections have been made.
Reviewer 2 Report
Comments and Suggestions for AuthorsThis manuscript seems to be an study to evaluated the oxidised aluminium origin of the AlSi10Mg and IN718 manufactured using laser fusion powder bed and subsequent they re-melted using laser. This study seems to be correctly carried out, but it is difficult to determine because the experimental setup and the results exposition is scarce. Additionally, the introduction is poor. For these reasons, the manuscript might be considered to be published after improving it using the following comments.
The literature review of the introduction part should be extended to clarify the novelty of the study. The author might use the following previous studies;
https://www.mdpi.com/1996-1944/14/2/393
https://link.springer.com/chapter/10.1007/978-981-10-1082-8_16
https://www.sciencedirect.com/science/article/pii/S0257897224001798
https://www.sciencedirect.com/science/article/pii/S2212827118307169
https://link.springer.com/article/10.1007/s00170-022-08840-x
The main outcomes of the study should be included in the end of the Introduction part to increase the dissemination of the manuscript.
The supplier of the products and devices should be included in 2. Materials and methods part because the reader can want to know a good supplier.
The details of the lasers (e.g., wavelength, CW or pulse, laser beam diameter, and laser beam quality) should be included in 2. Materials and methods part to increase the understanding of the study.
Subsections of the results such as topographical analyses, and chemical composition evaluation should be created in 3. Results part to clarify the results.
The following results needs an explain to increase the understanding of the findings;
Page 4
However, even for the Std and Low P-V conditions, the ratio of the melt-pool depth to width was larger than 0.5.
Page 7
Surfaces remelted with lower scanning speed (Key and Low P-V) had a larger area fraction of oxides.
Page 8
The bands at the melt-pool edges were quite thin, since these regions did not appear darker in backscattered electron images (Fig. 13), except for narrow regions at the edges
Page 9
(ii) oxide band at the melt-pool edge (O peak slightly higher than unmelted metal), (iii) thick oxide at the inner edge of the oxide band, and (iv) metal exposed region along the center of the melt pool (O peak hardly detected). For the keyholing condition, in region (iii) (thicker oxide) more spherical (less elongated) oxides were observed, and these oxides were more discontinuous than for the 179
other conditions.
Page 10
The keyholing condition resulted in more, but smaller particles. The lower-speed condition resulted in fewer particles, smaller than for the standard condition, and covering much less of the surface.
Page 10
t larger spherical oxides were observed at the higher beam power higher heat input (P/V ratio).
Page 14
. However, these increases in thickness are small compared with the total oxygen in the part. For example, taking the total oxygen content of the AlSi10Mg sample to be 400 ppm before melting, and using the melt-pool dimensions for standard conditions given in Table 6, the increase in oxide thickness would be approximately 60 nm if all of the internal oxygen were transferred to the surface as Al2O3.
An explain about why the IN718 is less susceptible to the oxidation should be included in the manuscript because it is an essential questions.
Author Response
Comment 1:
The literature review of the introduction part should be extended to clarify the novelty of the study. The author might use the following previous studies:
https://www.mdpi.com/1996-1944/14/2/393
https://link.springer.com/chapter/10.1007/978-981-10-1082-8_16
https://www.sciencedirect.com/science/article/pii/S0257897224001798
https://www.sciencedirect.com/science/article/pii/S2212827118307169
https://link.springer.com/article/10.1007/s00170-022-08840-x
Response: Reference to several of these papers has been added to the Introduction (references 8 & 9), and several citations added to the rest of the document including reference 15 from this list.
Comment 2: The main outcomes of the study should be included in the end of the Introduction part to increase the dissemination of the manuscript.
Response: Added (lines 44-46)
Comment 3: The supplier of the products and devices should be included in 2. Materials and methods part because the reader can want to know a good supplier.
Response: The IN718 supplier was added (line 52).
Comment 4: The details of the lasers (e.g., wavelength, CW or pulse, laser beam diameter, and laser beam quality) should be included in 2. Materials and methods part to increase the understanding of the study.
Response: Detail of the laser has been added to section 2.1.2 (lines 73-74)
Comment 5: Subsections of the results such as topographical analyses, and chemical composition evaluation should be created in 3. Results part to clarify the results.
Response: No change made. The existing sub-sections extend to three levels (e.g. section 3.2.1) and further subsections would be more confusing, in our opinion.
Comment 6:
The following results needs an explain to increase the understanding of the findings;
Page 4. However, even for the Std and Low P-V conditions, the ratio of the melt-pool depth to width was larger than 0.5.
Response: A comment has been added (lines 117-119).
Page 7. Surfaces remelted with lower scanning speed (Key and Low P-V) had a larger area fraction of oxides.
Response: A comment has been added (lines 150-155).
Page 8. The bands at the melt-pool edges were quite thin, since these regions did not appear darker in backscattered electron images (Fig. 13), except for narrow regions at the edges
Response: Additional wording has been added (lines 170-172).
Page 9. (ii) oxide band at the melt-pool edge (O peak slightly higher than unmelted metal), (iii) thick oxide at the inner edge of the oxide band, and (iv) metal exposed region along the center of the melt pool (O peak hardly detected). For the keyholing condition, in region (iii) (thicker oxide) more spherical (less elongated) oxides were observed, and these oxides were more discontinuous than for the other conditions.
Response: Additional wording has been added, to state the proposed origin of these regions (lines 203-209)
Page 10. The keyholing condition resulted in more, but smaller particles. The lower-speed condition resulted in fewer particles, smaller than for the standard condition, and covering much less of the surface.
Response: Additional clarification has been added (lines 219-220)
Page 10. t larger spherical oxides were observed at the higher beam power higher heat input (P/V ratio).
Response: This typographical error has been corrected (line 232)
Page 14. However, these increases in thickness are small compared with the total oxygen in the part. For example, taking the total oxygen content of the AlSi10Mg sample to be 400 ppm before melting, and using the melt-pool dimensions for standard conditions given in Table 6, the increase in oxide thickness would be approximately 60 nm if all of the internal oxygen were transferred to the surface as Al2O3.
Response: Additional explanation has been added (lines 298-304).
Comment 7: An explain about why the IN718 is less susceptible to the oxidation should be included in the manuscript because it is an essential questions.
Response: Additional discussion has been added, clarifying that there appears to be a difference in reworking on the sample surface, but no direct evidence on susceptibility to oxidation (lines 438-449).
Reviewer 3 Report
Comments and Suggestions for AuthorsThis study investigated mechanisms of oxide formation and distribution in the IN718 and AlSi10Mg bulk samples during LPBF process by varying the SLM process conditions. The morphology and thickness of oxides were well analyzed by optical microscopy, SEM and EDX. As a result of discussion on oxide inclusions formation, it was suggested that the spatter oxidation and oxides reworking were a main reason, and the effect of direct oxidation of the melt-pool surface was small. These achievements seem to be beneficial to controlling an amount, morphology and distribution of oxide in the LPBF materials, leading to improving their mechanical properties in the future. Thus, the manuscript is considered to be acceptable for publication, just after minor revisions, as listed below.
- In Fig.5 (c) and (d), the total amounts of energy of SLM process seem almost the same, as can be seen in Table 3, why was the melt pool area of (d) significantly larger than that of (c)?
- Regarding the question above, in Fig.10 (c) and (d), the total energy of SLM process of (d) is nearly twice that of (c), why was the melt pool area of these specimens almost the same?
- On p.17, line 409, “that on” → “than that on”.
Author Response
Comment 1: In Fig.5 (c) and (d), the total amounts of energy of SLM process seem almost the same, as can be seen in Table 3, why was the melt pool area of (d) significantly larger than that of (c)?
Discussion has been added, emphasizing that the melt-pool size depends on the P/V ratio (lines 119-122)
Comment 2: Regarding the question above, in Fig.10 (c) and (d), the total energy of SLM process of (d) is nearly twice that of (c), why was the melt pool area of these specimens almost the same?
Discussion added, noting the difference in the response of AlSi10Mg and IN718 (lines 162-166)
Comment 3: On p.17, line 409, “that on” → “than that on”.
Corrected
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThis manuscript is an study to evaluated the oxidised aluminium origin of the AlSi10Mg and IN718 manufactured using laser fusion powder bed and subsequent they re-melted using laser. The chemical composition and microstructures of the samples were correctly evaluated. The number of the parameters studied was the adequate to obtain the conclusions. For these reasons, the manuscript can be published after considering the following comments:
The wavelength of the lasers should be included in 2. Materials and methods part to increase the understanding of the study.
My specific comments are the following.
To add reference in line 209 of page 10 "the initially thin oxide at the melt-pool edge into more spherical particles [REF]."
To include reference in line 304 of page 14 "interior of the melt pool to its surface [REF]."
Author Response
Comment 1: The wavelength of the lasers should be included in 2. Materials and methods part to increase the understanding of the study.
Response: The wavelength is 1.06-1.1 µm; this has been added in lines 73-74.
Comment 2: To add reference in line 209 of page 10 "the initially thin oxide at the melt-pool edge into more spherical particles [REF]."
Response: I hope that I understood the comment correctly: I have added references to the relevant figures in lines 209-211.
Comment 3: To include reference in line 304 of page 14 "interior of the melt pool to its surface [REF]."
Response: I have reworded this section for clarity, adding the equations used to estimate the thickness (lines 303-318).
