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Microstructure and Mechanical Properties of a Novel Lightweight and Heat-Resistant Al-3.0Ce-0.9Ca-1.9Mn-1.2Zr Alloy Fabricated by Selective Laser Melting

Coatings 2025, 15(2), 247; https://doi.org/10.3390/coatings15020247

by Wanwen Zhang^1,2,3, Mengmeng Wang^1,*

, Xiaodan Yu⁴, Zhigang Zhang⁵, Dongting Cai⁶, Baoxiang Shen⁷, Jianzhou Long¹ and Yufeng Sun¹

Reviewer 1: Anonymous

Reviewer 2: Anonymous

Reviewer 3: Anonymous

Reviewer 4: Anonymous

Coatings 2025, 15(2), 247; https://doi.org/10.3390/coatings15020247

Submission received: 20 January 2025 / Revised: 12 February 2025 / Accepted: 13 February 2025 / Published: 19 February 2025

(This article belongs to the Special Issue Structural, Mechanical and Tribological Properties of Hard Coatings)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The researchers have prepared a very detailed and very technical paper on the Al-Ce-Ca-Mn-Zr alloy. I could not see any technical weaknesses or deficiencies in the article. The article is really very detailed. However, I suggest that they only take into account a few minor stylistic errors that I have mentioned below;

1)While the introduction mentions the challenges of anisotropy and room-temperature performance in Al-Ce alloys, it does not emphasize the severity of these limitations or their impact on real-world applications. (Suggestion :Add a more detailed discussion on how these challenges hinder the broader adoption of SLM-formed Al-Ce alloys in industrial applications.)

2)Expand on why Ca was chosen over other potential elements and how it complements the properties of Al-Ce alloys.
3) Avoid theoretical information when giving information about the powder size in the experimental work (e.g. small sized powders are not suitable for the SLM method).

4)In Figure 7 the photo looks blurred, better quality and larger photos can be provided.

5)Correct Figure 10-axis head (Hardness)

Author Response

Revising Report

First of all, I would like to express our sincere gratitude to the editor and reviewers for theircomments. These comments are all valuable and helpful for revising and improving our manuscriptas well as the important guiding significance to our researches. We have studied commentscarefully and have made correction which we hope meet with approval. The summary ofcorrections and the responses to the editor's and the reviewers' comments are listed below.

Summary of the revision:

Abstract & Section 1:

We have modified the numerical extraction in the abstract and title sections. We have rounded the values of tensile strength, yield strength, etc. in the article to the nearest integer, and kept the value of elongation at 0.1%. And the content was modified, emphasizing the properties and possible application scenarios of SLM formed Al-3.0Ce-0.9Ca-1.9Mn-1.2Zr alloy. In the abstract section, we supplemented relevant references for the statement of Ce content and eutectic transformation temperature of Al Ce alloy eutectic reaction. We have also explained why we attempted to modify Al Ce alloys with Ca elements.

Section 3(Method):

We have removed a large number of statements related to powder particle size distribution in this section. In the SLM forming process, we have supplemented the initial dimensions of SLM formed alloys. In terms of heat treatment process, we have supplemented the heat treatment equipment used, the heating rate in the heat treatment experiment, and the cooling method of the heat treatment. On the testing equipment, we have supplemented the XRD equipment model, microhardness testing method, strain measurement method in tensile testing, etc.

Section 4(Experimental Results):

We have added more analysis to delve deeper into the plasticity of the alloy, especially in terms of the mechanical properties and anisotropy of this type of high-temperature alloy. In addition, we have added statistical distribution maps of grain size in various cross-sections of the alloy before and after heat treatment to explain the effect of heat treatment on the grain size of the alloy. Considering language and grammar issues, including complex and difficult to understand sentences, we have made careful revisions.

Responses to editor and reviewers:

Comments 1: While the introduction mentions the challenges of anisotropy and room-temperature performance in Al-Ce alloys, it does not emphasize the severity of these limitations or their impact on real-world applications. (Suggestion :Add a more detailed discussion on how these challenges hinder the broader adoption of SLM-formed Al-Ce alloys in industrial applications.)

Response 1:Thank you very much for your valuable suggestion. As an emerging heat-resistant aluminum alloy, Al Ce alloy has a high eutectic point composition. What are the problems that can cause a decrease in the material's tensile properties, especially in high-temperature environments, and how can they hinder SLM forming. I have made modifications to the "Introduction" and added the sentence "... in severe cases, it can cause the alloy to fracture along the direction of poor mechanical properties in anisotropy, resulting in losses" to emphasize the importance of the current challenges and obstacles faced by Al Ce alloy in terms of its service range and application value. The sentence has been highlighted in red font. Thank you.

Comments 2：Expand on why Ca was chosen over other potential elements and how it complements the properties of Al-Ce alloys.

Response 2:Agree, thank you very much for your valuable suggestion. Due to the consideration of lightweight design and the valuable and cost-effective characteristics of Ca element, we are trying to achieve excellent mechanical properties, dense microstructure, and better plastic processing performance by adding Ca element. We include "Introduction" in the article, which discusses the role of Ca element in Al alloy. On the one hand, Ca element can lubricate the matrix, thereby improving the plasticity of Al Ce alloy, and on the other hand, it can effectively suppress ternary metalized compounds with poor symmetry. We have made the following modifications in the article to enhance the plastic processing capability of alloys and expand the application scenarios of Al Ce alloys, highlighting the unique performance and price advantages of Ca element. The modified parts have been highlighted in red font in the revised article.

Comments 3：Avoid theoretical information when giving information about the powder size in the experimental work (e.g. small sized powders are not suitable for the SLM method).

Response 3:Agree, thank you very much for your suggestion. In the article, small-sized satellite powders can affect the SLM formability of alloys. The statement 'small-sized powders are not suitable for SLM methods' is widely accepted and does not bring any new content to scientific research. Therefore, we have deleted this part of the revised article.

Comments 4：In Figure 7 the photo looks blurred, better quality and larger photos can be provided.

Response 4:Thank you for your valuable feedback. In the selection of process parameters for SLM forming Al Ce Ca Mn Zr alloy, we chose 40 μ m as the printing layer thickness. The microstructure produced under this printing layer thickness is very dense, and the melt pool has a very high boundary density. At the same time, the addition of Zr element further refines the columnar crystals at the center of the melt pool and the equiaxed crystals at the melt pool boundary, with an average grain size of only 2.5-5 microns. Therefore, in our repeated sample preparation and multiple photography processes, we were only able to find this set of SEM images, which can not only observe the boundaries of the melt pool relatively clearly, but also distinguish the distribution of columnar and equiaxed crystals inside the melt pool. In the EBSD images displayed in conjunction with it, the size and distribution images of columnar and equiaxed crystals in the melt pool can be observed more clearly. Thank you again for providing valuable feedback.

Comments 5：Correct Figure 10-axis head (Hardness)

Response 5:Thank you for pointing out this issue. We are very sorry for the mistake caused by our negligence in drawing, writing, and checking the paper. In the manuscript we returned, this error has been corrected. In the revised article, we highlighted the text before and after Figure 10 in red font.

Reference:

1.PLOTKOWSKI A, RIOS O, SRIDHARAN N, et al. Evaluation of an Al-Ce alloy for laser additive manufacturing [J]. Acta Materialia, 2017, 126: 507-519.

2.Ren Y, Dong P, Zeng Y, et al. Effect of heat treatment on properties of Al-Mg-Sc-Zr alloy printed by selective laser melting[J]. Applied Surface Science, 2022, 574: 151471.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The presented study, entitled "Microstructure and Mechanical Properties of a Novel Lightweight and Heat-resistant Al-Ce-Ca-Mn-Zr alloy fabricated by Selective Laer Melting", discusses the microstructure and mechanical properties of the Al-Ce-Ca-Mn-Zr alloy fabricated by selective laser melting (SLM). The study represents an interesting work with very nice processing, presentation and at the same time interesting and, in my opinion, beneficial results. Nevertheless, I have several questions and comments about the study and the authors:

1. Why did you choose these specific temperature values for testing (200,250, 300, 350?

2. What procedure did you choose to find the optimal values of the annealing temperature and holding time?

3. When comparing the changes in the monitored parameters with increasing temperature, I lack a statistical evaluation of the differences that arise in terms of applying differential statistical tests and calculating the corresponding values.

Overall, I consider the presented study to be beneficial and, after incorporating my comments, I recommend publishing it.

Author Response

Revising Report

Summary of the revision:

Abstract & Section 1:

Section 3(Method):

Section 4(Experimental Results):

Responses to editor and reviewers:

Comments 1: Why did you choose these specific temperature values for testing (200,250, 300, 350?

Response 1: Thank you for your correction. Compared to other types of alloys, heat-resistant aluminum alloys have a very low density and are often used as heat-resistant structural components in automotive engines and other fields. These temperatures are representative and are common service temperatures and testing temperatures in heat-resistant aluminum alloys. We have made the following modifications in the article: "Aluminum alloys, known for their excellent mechanical properties and corrosion resistance, are widely used in aerospace, automotive engines, and other industries", so that the test temperatures selected in the experimental section are representative. Thank you again for your correction. The modified parts have been highlighted in red font in the text. Thank you again for your correction.

Comments 2： What procedure did you choose to find the optimal values of the annealing temperature and holding time?

Response 2: Thank you. We use microhardness as an evaluation index for anisotropy and tensile strength of alloy materials as a mechanical property index, and study their elongation at high temperatures when testing alloys. The results showed that under the heat treatment parameters of holding time of 8 hours at 375 ℃, the alloy sample had the best mechanical properties and material plasticity. In order to better explain the content of this section, we have made some modifications to the article. We have added a paragraph in the revised article that reads "The samples under the annealing process of 375 ℃ and 8 hours of holding time have the best tensile properties and microhardness." The added paragraph has been highlighted in red font. Thank you again for pointing out this issue.

Comments 3：When comparing the changes in the monitored parameters with increasing temperature, I lack a statistical evaluation of the differences that arise in terms of applying differential statistical tests and calculating the corresponding values.

Response 3: Thank you for your suggestion. As this experimental study mainly focuses on the mechanical properties and processing plasticity of alloys, we have designed a set of experiments and found ideal experimental parameters, aiming to provide reference for the processing technology and heat treatment of Al Ce alloys. Deep level mathematical analysis is not our strong suit. We will continuously strengthen our knowledge of statistics and improve our statistical analysis of alloy properties in future work.

Reference:

1.PLOTKOWSKI A, RIOS O, SRIDHARAN N, et al. Evaluation of an Al-Ce alloy for laser additive manufacturing [J]. Acta Materialia, 2017, 126: 507-519.

2.Ren Y, Dong P, Zeng Y, et al. Effect of heat treatment on properties of Al-Mg-Sc-Zr alloy printed by selective laser melting[J]. Applied Surface Science, 2022, 574: 151471.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The paper presents the microstructure and mechanical properties of Al-Ce-Ca-Mn-Zr alloy manufactured by selective laser melting. The topic and a newly-developed alloy are quite interesting, however the manuscript has to be revised while several minor and major issues were detected, i.e.:

Abstract:

1.1. Please add the actual chemical composition of the investigated alloy, e.g. Al-3.0Ce-0.9Ca-1.9Mn-1.2Zr.

1.2. The yield strength and ultimate tensile strength values should be rounded to whole MPa, while elongation values to 0.1%.

Introduction:

2.1. Please add source of the statement in lines 69-71.

2.2. Line 92 - "tear resistance" is not clear

2.3. I suggest to present lines 95-100 as a new paragraph and expand the topic of the SLM-processed Al-Ce and Al-Ca alloys based on the literature references.

Experimental procedure:

3.1. Please consider erasing lines 116-125 while there are general commonly accepted statements that do not introduce anything new to the paper nor the scientific field.

3.2. Lines 149-151: How was the strain measured during tensile test (i.e. extensometer, DIC analysis, crosshead movement)? The geometry of room temperature samples (Figure 5) is not consistent with the description in the text.

3.3. What about the methodology of XRD analysis, hardness measurements and, most of all, the selection of annealing parameters?

Results and Discussion:

4.1. The grain size or other microstructural dimensions (melt pools distance etc.) should be rounded to whole um.

4.2. Caption of Figure 6 should be presented more clearly. I suggest to use "as-built" instead of "printed" as well as change expression "construction surface" and "scanning surface" to "XY" and "XZ" or horizontal/vertical. Please explain this nomenclature in the text.

4.3. Line 214 - "... after annealing at 375C for 8h with a laser energy density of 52.19 J/mm3" - It is not clear.

4.4. Line 224 - "Compared to the printed state, ..." - Please add SEM images of the as-built state in the Figure 7.

4.5. Lines 253-254: Are these differences in the grain size between as-built and annealed state are significant? What about statistical analysis? How many EBSD scans were performed or what was the scanning area?

4.6. Lines 288-296: This shifting of Al (111) peak is hardly visible in the Figure 9 - please add its higher magnification etc. Besides, it is not clear why it shifts firstly to higher and then to lower angles. Instead, please add and focus on the volume fraction of Al11Ce3 phase after annealing for a different time.

4.7. Hardness values should be rounded to whole HV values.

4.8. Lines 329 - "The dislocation density in the matrix decreased, contributing to an increase in hardness" - Please correct this statement.

4.9. I suggest to change order of the presented results. It is better to show firstly the hardness results to explain the annealing temperature, i.e. 375C ensures the best homogeneity of mechanical properties, and then the microstructure and XRD analysis of as-built and annealed samples. Besides, I am not sure if the authors should present the XRD data for 4 and 6 hours; I suggest to erase the 375C/4h and 375C/6h and focus on the different annealing temperature (325, 375 and 425C for 8h) by adding their XRD analysis. In such way, it would be easier to explain chosen processing parameters and show the main conclusions of the paper.

4.10. Line 342 - "... under a laser energy density of 52.52 J/mm3" - It is not clear.

4.11. YS and UTS values should be rounded to whole MPa while the elongation values to 0.1%.

Conclusions:

5.1. Lines 460-461: "The optimal heat treatment parameters for the alloy are annealing temperature of 375C and holding time of 8h" - The optimization process of annealing parameters has to be presented more clearly in the paper to support such conclusion.

Comments on the Quality of English Language

The paper is written rather clearly, but requires some minor English corrections. Please consider the proofreading by an English native speaker if possible.

Author Response

Revising Report

Summary of the revision:

Abstract & Section 1:

Section 3(Method):

Section 4(Experimental Results):

Responses to editor and reviewers:

Comments 1.1.: Please add the actual chemical composition of the investigated alloy, e.g. Al-3.0Ce-0.9Ca-1.9Mn-1.2Zr.

Response 1: Thank you very much for providing this valuable suggestion. Adding the chemical composition of the alloy before each element will undoubtedly increase the standardization of the article. We have replaced all alloy names "Al-Ce-Ca-Mn-Zr" in the title, introduction, and main body of the revised manuscript with "Al-3.0Ce-0.9Ca-1.9Mn-1.2Zr". Thank you for your valuable feedback.

Comments 1.2： The yield strength and ultimate tensile strength values should be rounded to integer MPa, and the elongation value should be rounded to 0.1%.

Response 1.2:Agree, we did a very poor job in rounding, which undoubtedly greatly reduced the standardization of this article. In the revised document, we have carefully reviewed this work, rounding all yield strength values and tensile strength values to integer MPa, and rounding all elongation values to 0.1%. We have made improvements to all areas where the reserved digits need to be modified. Thank you for pointing out this issue.

Comments 2.1： Please add source of the statement in lines 69-71.

Response 2.1: Agree, we are very sorry that we overlooked the addition of reference materials when stating the eutectic point and eutectic transition temperature of Al Ce alloy. L54 to 60 do indeed require the addition of some reference materials, so we have added references in the hope of improving the rigor of this study. At the same time, we have added the above-mentioned literature to the revised document and highlighted it in the text. Thank you very much for your correction.

Comments 2.2：Line 92 - "tear resistance" is not clear

Response 2.2: Agree, thank you for pointing out this issue. Due to the decrease in elongation at high temperatures, which leads to a reduction in material plasticity and seriously damages the performance of the alloy, making it difficult for the material to meet service requirements in high-temperature environments, we have made corrections in the revised article and highlighted it in red font. Thank you again for pointing out this issue.

Comments 2.3：I suggest to present lines 95-100 as a new paragraph and expand the topic of the SLM-processed Al-Ce and Al-Ca alloys based on the literature references.

Response 2.3: Agree, thank you for your valuable suggestion. Compared to traditional Al Si alloys, Al Mg alloys, and Al Cu alloys, SLM formed Al Ce alloys and Al Ca alloys are relatively novel topics. The research on SLM processed Al Ce alloys and Al Ca alloys is not yet mature. The research literature we have found in this area is not representative, so it is currently difficult for us to write valuable content on SLM forming Al Ce and Al Ca as the main themes. SLM formed Al Ce alloy has excellent heat resistance, so this is a very important direction for our future work. Thank you again for your valuable suggestions.

Comments 3.1：Please consider erasing lines 116-125 while there are general commonly accepted statements that do not introduce anything new to the paper nor the scientific field.

Response 3.1: Thank you very much for your valuable suggestions, and we apologize that our writing included this widely accepted content, which made this article somewhat cumbersome. The influence of powder particle size distribution on SLM forming quality is irrelevant to this article. Therefore, we have removed the optional content from lines 116-125 in the original article in order to make it more concise.

Comments 3.2： Lines 149-151: How was the strain measured during tensile test (i.e. extensometer, DIC analysis, crosshead movement)? The geometry of room temperature samples (Figure 5) is not consistent with the description in the text.

Response 3.2: Agree, we are very sorry for missing the method of strain measurement in the article. During the writing process, we omitted the optical extensometer used during the tensile test. The model of the extensometer has been supplemented in the experimental method section of the revised article and highlighted in red font. Thank you again for pointing out this issue. At the same time, we have corrected the description of the incorrect size of the gauge length section of the room temperature stretching sample, which resulted in the inconsistency between the text and images, and highlighted it in red font. Thank you.

Comments 3.3：What about the methodology of XRD analysis, hardness measurements and, most of all, the selection of annealing parameters?

Response 3.3: Thank you for your valuable suggestion. We apologize for the omission of XRD analysis software (Jade 9.0), microhardness measuring instruments (including testing conditions, loads, etc.), and the crucial annealing method in the experimental methods section of our article. We have made the following modifications in the revised article:

In the experimental methods section of the article, we supplemented the XRD analysis method, added information about the software used for XRD analysis (Jade 9.0), as well as the model and testing conditions of the microhardness measuring instrument. In the revised article, this section has been highlighted in red font.

2.) We have added a testing method for microhardness, using the TMVS-1 Vickers hardness tester with a loading force of 500g and a loading time of 10s. The additional information has been highlighted in red font in the article. Thank you again for your valuable suggestion.

3.) We annealed the alloy samples using the Kejing KSL-1100X-S muffle furnace. The heating rate of the muffle furnace was 10 degrees Celsius/min. When the temperature reached the predetermined temperature, the samples were cooled by water and placed in the muffle furnace for heating. This section has been supplemented in the revised article and highlighted in red font.

Comments 4.1：The grain size or other microstructural dimensions (melt pools distance etc.) should be rounded to whole um

Response 4.1: We apologize again for the lack of standardization in our accuracy. In the revised manuscript, we have rounded all microstructure dimensions such as melt pool distance to whole micrometers. We have marked the areas that need to be changed in red font for the digit extraction (where tensile strength, yield strength, microhardness, microstructure of the melt pool, etc. have been rounded to integers, and where elongation is used, we have rounded to 0.1%). In terms of grain size, due to the rapid melting and solidification characteristics of SLM, this is a very small equiaxed crystal that is close to the sub micron level and in the heat affected zone. Therefore, we choose to cut it to two decimal places. We apologize again for the lack of standardization in our digit extraction.

Comments 4.2：Caption of Figure 6 should be presented more clearly. I suggest to use "as-built" instead of "printed" as well as change expression "construction surface" and "scanning surface" to "XY" and "XZ" or horizontal/vertical. Please explain this nomenclature in the text.

Response 4.2: Thank you very much for your valuable suggestion. We deeply apologize for the negligence caused in our writing process. We overlooked the consistency of the naming of the test section in the article, and we have made modifications to the caption of Figure 6. And the following explanations were provided in the main text to provide a clearer explanation of specific cross-sections in SLM forming processes. We have made the following changes in the revised article:

"Printed" has been changed to "as build", and the modified part has been highlighted in red font in the text.

2.) We have changed the caption of Figure 6 from the original "construction surface" and "scanning surface" to "XY plane" and "XZ plane", and the modified parts have been highlighted in red font in the revised article.

Comments 4.3：Line 214 - "... after annealing at 375C for 8h with a laser energy density of 52.19 J/mm3" - It is not clear.

Response 4.3: Compared to SLM forming process parameters, this study focuses on the post-treatment performance of SLM formed Al Ce alloy samples. In the article, the phrase '... 52.19 J/mm3 laser energy density' has been changed to 'under laser power of 380W'. As this article mainly explores the effect of annealing process on the properties of alloys, there is no explanation of the calculation formula for laser energy density or the concept in the article. We have revised this statement and highlighted it in red font in the text.

Comments 4.4：Line 224 - "Compared to the printed state, ..." - Please add SEM images of the as-built state in the Figure 7.

Response 4.4: Thank you very much for pointing out this issue. In the process parameters of SLM forming Al-3.0Ce-0.9Ca-1.9Mn-1.2Zr alloy, we chose a very low printing layer thickness (40 microns) and a very high scanning speed (1400mm/s), and adopted a scanning strategy of interlayer 67 ° tilt angle. Therefore, the distribution of the alloy's melt pool is very disordered. Through repeated sample preparation and multiple shooting, we found that this group can clearly observe the boundary distribution of the melt pool, as well as the areas of columnar and equiaxed crystals in the annealed state. After multiple attempts, we did not find the melt pool boundary of the original printed alloy, so we made significant modifications to this part and displayed it in highlighted red font. Thanks again.

Comments 4.5：Lines 253-254: Are these differences in the grain size between as-built and annealed state are significant? What about statistical analysis? How many EBSD scans were performed or what was the scanning area?

Response 4.5: Yes, thank you. The original printed and annealed states of this type of Al-3.0Ce-0.9Ca-1.9Mn-1.2Zr alloy have different average grain sizes, which are generated by the rapid melting and solidification characteristics of SLM, resulting in micrometer to submicron and grain structures. Due to the different temperature gradients in the SLM process, the metallurgical bonding quality of the alloy melt pool in various directions and regions may vary to some extent (specifically manifested as the formation of small equiaxed crystal regions at the melt pool boundary and columnar crystals at the melt pool center). The EBSD scanning area we selected is 200 μ m * 200um, and a complete melt pool can be observed in both the XY and XZ planes. We chose 2.5um as the scanning step size. We have made the following modifications in the revised article, hoping to make this part of the content clearer:

In the EBSD chart, a statistical graph of the corresponding grain size distribution has been added, hoping to more intuitively display the micrometer to submicron grain size of the new lightweight heat-resistant Al Ce alloy formed by this SLM process. It has been shown in the image of the revised manuscript.

2.) We have made modifications to the experiments and methods section of the article, further describing more details of the EBSD experiment, including the areas scanned by the alloy (including explanations of the XY section and XZ interface). There are also test parameters selected for EBSD testing of Al-3.0Ce-0.9Ca-1.9Mn-1.2Zr alloy, including scanning range, scanning step size, etc. It has been presented in the manuscript and highlighted in font.

3) In the SLM formed samples of this type of alloy in the article, there is a certain degree of recrystallization phenomenon in the original printed state alloy and annealed state alloy, especially in the columnar crystal region at the center of the melt pool, which is often accompanied by fracture in the long axis direction. Therefore, we have made modifications to the article and described it in red highlighted font.

Comments 4.6：Lines 288-296: This shifting of Al (111) peak is hardly visible in the Figure 9 - please add its higher magnification etc. Besides, it is not clear why it shifts firstly to higher and then to lower angles. Instead, please add and focus on the volume fraction of Al11Ce3 phase after annealing for a different time.

Response 4.6: Thank you. In the analysis of the XRD diffraction pattern, we neglected to enlarge the image, resulting in the Al (111) peak shift of the alloy being almost invisible. In the revised article, we made modifications by enlarging the image of the Al (111) diffraction peak area. Under the magnification, the Al (111) diffraction peak can be clearly seen. The volume fraction of Al11Ce3 phase before and after annealing has also been a concern for us. Due to the solid solution of a large amount of Ce, Mn, Zr and other elements in the α - Al matrix of Al-3.0Ce-0.9Ca-1.9Mn-1.2Zr alloy formed by SLM in both the original printed and annealed states, we inferred the interplanar spacing of α - Al in the alloy by analyzing the diffraction angle of Al (111) planes, and qualitatively analyzed the solid solubility of various elements in Al-3.0Ce-0.9Ca-1.9Mn-1.2Zr alloy before and after annealing treatment. In the revised article, we enlarged the diffraction peaks of the Al (111) crystal plane at an appropriate magnification, and highlighted the text before and after the modified images.

Comments 4.7：Hardness values should be rounded to whole HV values.

Response 4.7: We apologize again for the lack of standardization in our accuracy. In the revised manuscript, we have rounded all microstructure dimensions such as melt pool distance to whole micrometers. We have marked all the areas where the numbers need to be changed in red font (where tensile strength, yield strength, microhardness, microstructure size of the melt pool, etc. have been rounded to integers, and where elongation is used, we have rounded to 0.1%). In terms of grain size, due to the rapid melting and solidification characteristics of SLM, this is a very small equiaxed crystal that is close to the sub micron level and in the heat affected zone. Therefore, we choose to cut it to two decimal places. We apologize again for the lack of standardization in our digit extraction.

Comments 4.8：Lines 329 - "The dislocation density in the matrix decreased, contributing to an increase in hardness" - Please correct this statement.

Response 4.8: Thank you very much for pointing out the issue. We deeply apologize for the error caused during our writing process and have corrected the statement in the article.

Comments 4.9： I suggest to change order of the presented results. It is better to show firstly the hardness results to explain the annealing temperature, i.e. 375C ensures the best homogeneity of mechanical properties, and then the microstructure and XRD analysis of as-built and annealed samples. Besides, I am not sure if the authors should present the XRD data for 4 and 6 hours; I suggest to erase the 375C/4h and 375C/6h and focus on the different annealing temperature (325, 375 and 425C for 8h) by adding their XRD analysis. In such way, it would be easier to explain chosen processing parameters and show the main conclusions of the paper.

Response 4.9: Thank you very much for these two valuable suggestions. We conducted XRD analyses for 325/8h, 375/8h, and 425/8h, and the results showed that different annealing temperatures had almost no effect on the diffraction peaks of the alloy. On the contrary, the data sets of 375/4 h, 375/6 h, and 375/8h will produce significant shifts in diffraction peaks, making them more valuable. Therefore, we consider presenting this set of data with different insulation times in the hope of increasing the richness and value of the research content, making this article more comprehensive. Thank you very much again for your suggestion.

Comments 4.10： Line 342 - "... under a laser energy density of 52.52 J/mm3" - It is not clear.

Response 4.10: Compared to SLM forming process parameters, this study focuses on the post-treatment performance of SLM formed Al Ce alloy samples. In the article, the phrase '... 52.19 J/mm3 laser energy density' has been changed to 'under laser power of 380W'. As this article mainly explores the effect of annealing process on the properties of alloys, there is no explanation of the calculation formula for laser energy density or the concept in the article. We have revised this statement and highlighted it in red font in the text.

Comments 4.11： YS and UTS values should be rounded to whole MPa while the elongation values to 0.1%

Response 19: Thank you for pointing out the issue. We have done a very inappropriate job in truncating the digits. We have rounded a large number of values to two decimal places. In the revised article, we have standardized the truncating digits of these values (including tensile strength, yield strength, microhardness, microstructure size of the melt pool, etc., all rounded to integers, and where elongation is used, we rounded to 0.1%). We have also rounded the integers Mpa for YS and UTS in the main text, and rounded to 0.1% for elongation. The numerical parts of all modified YS and UTS values in the article have been highlighted in red. Once again, we have rounded the digits to this point. We apologize for the lack of standardization in this aspect, and we will keep this detail in mind in our future work, This good habit is undoubtedly beneficial for scientific research. Thanks again.

Comments 5.1：Lines 460-461: "The optimal heat treatment parameters for the alloy are annealing temperature of 375C and holding time of 8h" - The optimization process of annealing parameters has to be presented more clearly in the paper to support such conclusion.

Response 5.1: Thank you for pointing out this issue. We have added a paragraph in the revised article that reads "Under these three annealing processes, the samples were annealed at 375 ℃ and held for 8 hours, while maintaining the best tensile properties and microhardness." The added paragraph has been highlighted in red font. Thank you again for pointing out this issue.

Content:The paper is written rather clearly, but requires some minor English corrections. Please consider the proofreading by an English native speaker if possible.

Response: Considering language and grammar issues, including complex and difficult to understand sentences, we have made careful revisions.

Reference:

1.PLOTKOWSKI A, RIOS O, SRIDHARAN N, et al. Evaluation of an Al-Ce alloy for laser additive manufacturing [J]. Acta Materialia, 2017, 126: 507-519.

2.Ren Y, Dong P, Zeng Y, et al. Effect of heat treatment on properties of Al-Mg-Sc-Zr alloy printed by selective laser melting[J]. Applied Surface Science, 2022, 574: 151471.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This article aims at investigating the microstructure and mechanical properties of Al-Ce-Ca-Mn-Zr alloy produced by LPBF. A “multiscale” microstructure characterization is provided. Mechanical properties are investigated by hardness after different heat treatment and tensile tests at different temperatures. Results are well explained however some questions remains :

-L46-53 and L54 to 60 please add some references
-L129-132 is Al11Ce3 detected ?
-L150 what is the furnace type and heating conditions, strain measurement technique for tensile test at high temperature ?
-experimental methods : information’s concerning hardness tests are missing
- L152 what is the initial SLM samples size ?
-L180-181 result about crystal size is not obvious. Crystal size should be mentioned
-L288-291 please provide a zoom around (111) peak to see the shift
-Fig 11 any comment about reproducibility ?
-what about health matters ?
-why do you observe a bimodal grain distribution ? is it common for LPBF Al alloys ? What about texture ?
-what about hardness variation in one plane ? does the bimodal distribution of grain lead to hardness variations ?
-there is one ref (to Fig 12) is the result and discussion part can be renamed as result part or can you discuss the results with the literature ?

Minor editing errors
-title : miss the s or “laser”
-abstract : results without decimal will increase the readability
-table 3 : there is 2 times the same temperature
-Fig 3 and 9 It should be useful to specify either in the figure or the caption at which phase corresponds PDF lines. Al11Ce3 symbols seems to be shifted compare to ref
-Fig 14 it is difficult to read the annotation on the micrographies, globally this figure has a poor readability

Author Response

Revising Report

Summary of the revision:

Abstract & Section 1:

Section 3(Method):

Section 4(Experimental Results):

Responses to editor and reviewers:

Comments 1: -L46-53 and L54 to 60 please add some references

Response 1: Very sorry, we overlooked the addition of reference materials when stating the eutectic point and transformation temperature of Al Ce alloy. L54 to 60 indeed require some reference materials, so we have added references in the hope of improving the rigor of this study. At the same time, we have added the above-mentioned literature to the revised document and highlighted it in the text. Thank you very much for your correction.

Comments 2：-L129-132 is Al11Ce3 detected ?

Response 2: Thank you very much for your correction. Due to the low content of Ce element, there are only very small diffraction peaks. Therefore, the main approach is to analyze the variation of interplanar spacing in the α - Al matrix of the Al (111) alloy before and after annealing, in order to infer the changes in the internal microstructure of the alloy before and after annealing. We have supplemented this section in the revised article and highlighted it in red font. Thank you for your correction.

Comments 3：L150 what is the furnace type and heating conditions, strain measurement technique for tensile test at high temperature ?

Response 3: Thank you very much for your valuable feedback. We are very sorry that during our writing process, we overlooked the equipment and heating conditions for the heat treatment process, as well as the strain measuring instruments used in the tensile test. For the heat treatment test of the alloy, we used the GSL-1100X-S muffle furnace to heat the Al Ce Ca Mn Zr alloy. The heating rate during the test was 10 ℃/min, and the cooling method was water cooling. The strain measuring instrument uses an optical extensometer. It has been supplemented in the revised article. The supplementary parts have been highlighted in red font in the revised article. Thank you again for your valuable feedback.

Comments 4：experimental methods : information’s concerning hardness tests are missing

Response 4: Thank you very much for providing valuable suggestions. We are very sorry for missing the content about hardness testing during the writing process. We have selected the TMVS-1 Vickers hardness tester with a loading force of 500g and a loading time of 10s. In the revised article, the experimental methods section has been supplemented with the hardness testing instruments used, as well as our method of testing microhardness and the load tested. The modified part has been highlighted in red font in the revised article.

Comments 5：L152 what is the initial SLM samples size ?

Response 5: Thank you very much for your valuable feedback. During the writing process, we overlooked information regarding the initial sample size. The initial sample size of SLM is a cylindrical body with a diameter of 30mm and a height of 11mm. It has been explained in the text that information about sample size has been highlighted in red font in the revised article. Thank you again for providing valuable feedback.

Comments 6：L180-181 result about crystal size is not obvious. Crystal size should be mentioned

Response 6: Yes, thank you. The original printed and annealed states of this type of Al-3.0Ce-0.9Ca-1.9Mn-1.2Zr alloy have different average grain sizes, which are generated by the rapid melting and solidification characteristics of SLM, resulting in micrometer to submicron and grain structures. Due to the different temperature gradients in the SLM process, the metallurgical bonding quality of the alloy melt pool in various directions and regions may vary to some extent (specifically manifested as the formation of small equiaxed crystal regions at the melt pool boundary and columnar crystals at the melt pool center). The EBSD scanning area we selected is 200 μ m * 200um, and a complete melt pool can be observed in both the XY and XZ planes. We chose 2.5um as the scanning step size. We have made the following modifications in the revised article, hoping to make this part of the content clearer:

In the EBSD chart, a statistical graph of the corresponding grain size distribution has been added, hoping to more intuitively display the micrometer to submicron grain size of the new lightweight heat-resistant Al Ce alloy formed by this SLM process. It has been shown in the image of the revised manuscript.

Comments 7：L288-291 please provide a zoom around (111) peak to see the shift

Response 7: Thank you. In the analysis of the XRD diffraction pattern, we neglected to enlarge the image, resulting in the Al (111) peak shift of the alloy being almost invisible. In the revised article, we made modifications by enlarging the image of the Al (111) diffraction peak area. Under the magnification, the Al (111) diffraction peak can be clearly seen. The volume fraction of Al11Ce3 phase before and after annealing has also been a concern for us. Due to the solid solution of a large amount of Ce, Mn, Zr and other elements in the α - Al matrix of Al-3.0Ce-0.9Ca-1.9Mn-1.2Zr alloy formed by SLM in both the original printed and annealed states, we inferred the interplanar spacing of α - Al in the alloy by analyzing the diffraction angle of Al (111) planes, and qualitatively analyzed the solid solubility of various elements in Al-3.0Ce-0.9Ca-1.9Mn-1.2Zr alloy before and after annealing treatment. In the revised article, we enlarged the diffraction peaks of the Al (111) crystal plane at an appropriate magnification, and highlighted the text before and after the modified images.

Comments 8：Fig 11 any comment about reproducibility ?

Response 8: Thank you for pointing out the issue. We did not provide any comments on the reproducibility of Figure 11 in our article. We have further elaborated on the superplasticity exhibited by this alloy. Thank you again for pointing out this issue. In the revised article, we have highlighted this modification in red font. Thank you very much for providing valuable feedback.

Comments 9：what about health matters ?

Response 9: In human daily life, Al alloy can be seen everywhere, and its shadow can be found everywhere. The view on whether Al alloy is harmful to the human body seems to be uncommon.

Comments 10：why do you observe a bimodal grain distribution ? is it common for LPBF Al alloys ? What about texture ?

Response 10: This bimodal grain structure often appears in Al alloys with added elements such as Zr. The addition of Zr element will form heterogeneous nucleation points, resulting in a bimodal grain distribution. Traditional AlSi10Mg and AlSi7Mg alloys do not exhibit bimodal grain structures in LPBF forming processes. Further detailed explanations have been provided in the revised article, and a reference [33] has been added, highlighted in red font in the revised article.

Comments 11：what about hardness variation in one plane ? does the bimodal distribution of grain lead to hardness variations ?

Response 11: Agree, obviously, studying the influence of hardness changes and grain bimodal distribution on hardness changes on a plane is very valuable research, and we are also trying to conduct research and experiments in this area. Due to the selection of a 67 ° interlayer deflection angle in the SLM process parameters and the exploration of annealing processes under different regimes, it is expected to eliminate the anisotropy caused by the different metallurgical bonding qualities in the horizontal and vertical directions of the alloy. Therefore, this study did not focus on the influence of hardness changes on a plane and the bimodal distribution of grains on hardness changes. In future research, we will definitely focus on the hardness changes of alloys on a plane. Thank you again for your valuable suggestion.

Comments 12：there is one ref (to Fig 12) is the result and discussion part can be renamed as result part or can you discuss the results with the literature ?

Response 12: Thank you very much for your valuable suggestion. This article attempts to add Ca element in order to improve the plasticity performance of the alloy. Figure 12 shows that the elongation of this type of alloy increases significantly with the increase of temperature, demonstrating that this type of Al Ce Ca Mn Zr alloy exhibits certain superplasticity. The influence of Ca element on the plasticity of the alloy is an important direction for our future work, and we look forward to making progress in this field. We have added relevant discussions in the revised article and highlighted them in red font. Thank you again.

Comments 13：title : miss the s or “laser”

Response 13: We are very sorry for the mistake we made in spelling the words. We have corrected it and checked the spelling of the article again to ensure that there are no spelling errors in the text

Comments 14：results without decimal will increase the readability

Response 14: We are very sorry that we did not go into detail in standardizing and optimizing the decimal point. Thank you for pointing out the issue. We did a very inappropriate job in truncating the number of decimal places. We truncated a large number of values to the last two decimal places. In the revised article, we standardized the number of decimal places for these values (including tensile strength, yield strength, microhardness, melt pool microstructure size, etc., all rounded to integers, and for elongation, we rounded to 0.1%). We have rounded the integer Mpa for YS and UTS in the main text, and rounded the elongation to 0.1%. All modified YS and UTS values in the article are rounded to integers. We apologize again for the lack of standardization in our digit extraction, as some parts have been highlighted in red, We will keep this detail in mind in our future work, and this good habit is undoubtedly beneficial for scientific research.

Comments 15：table 3 : there is 2 times the same temperature

Response 15: Thank you, there are two instances of 325 ℃ in Table 3, which are not repeated. The first line below the column line represents 325 ℃, with a holding time of 0 hours, to indicate the original printed state of Al Ce Ca Mn Zr alloy without annealing treatment. Considering the possibility of misunderstanding, the first line below the column line has been changed to an annealing temperature of 20 ℃ and a holding time of 0 hours, and highlighted in red font. I hope this modification can improve the readability of the article.

Comments 16：Fig 3 and 9 It should be useful to specify either in the figure or the caption at which phase corresponds PDF lines. Al11Ce3 symbols seems to be shifted compare to ref

Response 16: Thank you very much for pointing out this issue. We have selected Al11Ce3 with a subscript. We have made modifications to Figure 3 and Figure 9 to address the issue of symbol offset in Al11Ce3, by adjusting the offset weight in the table below the Al11Ce3 numbers. Thank you again for your valuable suggestion. We have made revisions to the article and highlighted the text before and after Figure 3 and Figure 9 in red.

Comments 17：Fig 14 it is difficult to read the annotation on the micrographies, globally this figure has a poor readability

Response 17: We apologize for the insufficient attention to detail in our mapping, and thank you very much for your suggestions. The room temperature tensile port morphology of both the original printed and annealed samples in Figure 14 exhibits a large number of dimples, demonstrating good plasticity. The readability of Figure 14 is poor. We have made modifications to the annotations in Figure 14 to make them more prominent. We have added a white background to the annotation section of Figure 14 to make it easier to read. At the same time, we have highlighted the text before and after Figure 14 in red font to highlight the modifications made to Figure 14. Thank you again for your valuable feedback.

Reference:

1.PLOTKOWSKI A, RIOS O, SRIDHARAN N, et al. Evaluation of an Al-Ce alloy for laser additive manufacturing [J]. Acta Materialia, 2017, 126: 507-519.

2.Ren Y, Dong P, Zeng Y, et al. Effect of heat treatment on properties of Al-Mg-Sc-Zr alloy printed by selective laser melting[J]. Applied Surface Science, 2022, 574: 151471.

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have made most of the suggested revisions, however some minor aspect is still not entirely clear, i.e.:

Ad. 5.1.: I could not find the paragraph that has been mentioned by the authors as added, i.e. "Under these three annealing processes, ...". Besides, it is still not clear how the annealing parameters were optimized in the paper. The hardness and tensile results proved the best annealing temperature (i.e. 375C), but the annealing time and the procedure of its optimization is still not clear. The paragraph summarizing the selection of processing parameters (temperature and time) as well as the whole idea would be helpful.

Author Response

Revising Report

First of all, I would like to express our sincere gratitude to the editor and reviewers for their comments. These comments are all valuable and helpful for revising and improving our manuscript as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. The summary of corrections and the responses to the editor's and the reviewers' comments are listed below.

Summary of the revision:

Minor modifications have been made to the annealing process and related descriptions of the alloy.

Responses to editor and reviewers

Comments 1: Ad. 5.1.: I could not find the paragraph that has been mentioned by the authors as added, i.e. "Under these three annealing processes, ...". Besides, it is still not clear how the annealing parameters were optimized in the paper. The hardness and tensile results proved the best annealing temperature (i.e. 375C), but the annealing time and the procedure of its optimization is still not clear. The paragraph summarizing the selection of processing parameters (temperature and time) as well as the whole idea would be helpful.

Response 1: Thank you for point this out, and at the same time, thank you very much for your valuable suggestions.

1）We are deeply sorry for this negligence. When revising the article, we further modified the phrase " Under these three annealing processes, ..." to read " The samples under the annealing temperature of 375℃ and holding time of 8 hours have both the best tensile properties and microhardness.”, Causing you to be unable to find this paragraph in the revised article. Sorry again. Meanwhile, we have removed this sentence from the latest revised article.

2）We are also sorry that the design of annealing process in this article was not comprehensive enough. On the one hand, the sample size of the annealing process parameters we set is very limited, and only the mechanical properties of the samples at three different heat treatment temperatures under an 8-hour holding time were tested. We tested the XRD of three samples with different insulation times, and based on the XRD test data, we briefly analyzed the phase changes of the alloy with the extension of annealing time. We designed these two sets of experiments with different insulation times and different heat treatment temperatures independently of each other. We apologize again for this imperfect aspect.

3）Sorry again, this article did not cover the optimization process of annealing time, which is exactly the direction of our future work.

4）Thank you for your valuable suggestion. We have divided the summary of annealing process parameters to a certain extent, which are included in conclusions (2) and (3).

Thank you very much.

We have made the following modifications to the article:

1) The purpose of annealing (including eliminating residual stress and further improving alloy properties) was added under the Experimental procedure.

2) Under Conclusion, we made some modifications, namely " When the holding time is 8 h, as the annealing temperature increases, the mechanical properties of the alloy first increase and then decrease. The sample annealed at 375℃ has the best tensile properties.”

3) We have removed the last sentence, which reads: “The samples under the annealing temperature of 375℃ and holding time of 8 hours have both the best tensile properties and microhardness.”

Thank you again.

Best regards.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Dear authors,

Thank you to answer my comments and the great improvement of the manuscript.

My comments 9 was miserderstood I was refering to materials health matters. Al alloys made by SLM ofter show high amount of pore and depending composition can be crack sensitive. What about your alloy ?

Best regards,

Author Response

Revising Report

First of all, I would like to express our sincere gratitude to the editor and reviewers for their comments. These comments are all valuable and helpful for revising and improving our manuscript as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. The summary of corrections and the responses to the editor's and the reviewers' comments are listed below.

Summary of the revision:

Minor modifications have been made to the annealing process and related descriptions of the alloy.

Responses to editor and reviewers

Comments 1: My comments 9 was miserderstood I was refering to materials health matters. Al alloys made by SLM ofter show high amount of pore and depending composition can be crack sensitive. What about your alloy ?

Response 1: Thank you for point this out. Based on our work experience, we predicted and considered the crack sensitivity of the alloy at the beginning of its design. The results showed that this type of alloy did not have significant crack sensitivity. We used Pandat software to calculate the thermal cracking influencing factors, phase fraction, solid solubility and other parameters of the alloy, and conducted a comprehensive analysis of various indicators. Based on this, we designed a lightweight heat-resistant alloy. Regarding the metallurgical defects of alloys, this type of alloy has a certain distribution of metallurgical defects under various SLM parameters. The following are some of the high-throughput calculations conducted during our alloy design, which show that this type of alloy has a very low tendency towards hot cracking. And during the SLM forming experiment, we did not observe any obvious cracks.

The following is our high-throughput calculation method, which is based on the manual provided by Pandat software.

This type of alloy has certain metallurgical defects, with a certain distribution of porosity and incomplete fusion defects. The following are the metallographic images of this type of alloy taken after SLM forming. The results show that by adjusting certain parameters, we have obtained alloys with good forming quality (almost without any cracks).

According to our research, we have found in the experiment that if the SLM formed alloy is an Al-Cu alloy, there will be a lot of cracks in the alloy (distributed in a network like pattern over a large area). There are fewer cracks found in other types of alloys (Al-Si, Al-Mg). Eliminating metallurgical defects in SLM formed alloys has always been an important direction of our research, and we always hope to obtain formed samples with very good density. This article focuses on studying the annealing system and mechanical properties of alloys, so we believe that the above work content should not be included in this article.

Thank you very much.

Best regards.

Author Response File: Author Response.pdf

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Microstructure and Mechanical Properties of a Novel Lightweight and Heat-Resistant Al-3.0Ce-0.9Ca-1.9Mn-1.2Zr Alloy Fabricated by Selective Laser Melting

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