Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript reports on an assessment of the latent heat of hypoeutectic AlSiCu alloys, with Cu content varying from 1% to 4% by mass by combining experimentation by DSC, with analytical methods of thermal analysis via cooling curve measurements and thermodynamic computer calculations using JMatPro and Thermo-Calc. The study claims to find reasonable agreement between the experimentally determined values and the predictions of the computational calculations for the latent heat of the alloys of differing Cu concentrations. The largest differences between experimental results and computer calculation predictions obtained for Thermocalc software use and was attributed primarily to specifics of the respective thermodynamic database utilized. The manuscript implicitly attempts to address a basic challenge associated with experimental measurements of thermophysical properties by DSC for inhomogeneous alloys that intrinsically stem from the small scale (mass ≤ 30 mg) of the samples, which can introduce significant nonsystematic error, limits accuracy and introduces variability to the experimental results. While interesting, a major shortcoming of the manuscript stems from the lack of discussion and attempt of rationalization of the systematic disagreement between the experimental results from DSC and the cooling curve data analysis and the predictions of the thermodynamic computer calculations regarding the effects of Cu concentration on latent heat values of the alloys. The experiments indicate an increase of the latent heat with an increase in the Cu concentration from 1 wt% to 4 wt%, while Thermo-Calc and JMatPro indicate the opposite trend, a decrease of the latent heat with increasing. THE MANUSCRIPT NARRATIVE fails to address this fundamental disagreement. This qualitative and fundamental discrepancy between results from experiments and computations renders questionable the value of the presented discussion of the numerical differences of the latent heats obtained for the different alloy compositions. THIS is a major shortcoming, detracts from the quality and value of the contribution and must be remedied. Recommendation – Mandatory Revision.

 

An incomplete list of some examples of specific points that are problematic and detract from the quality of the manuscript and need to be addressed, clarified, corrected etc… in any revision follows:

 

P4 –L 132/133: Why stating AlSi7Cu1? Compositions in Table 1 all appear to indicate alloys of the tyoe Al5CuCux?  Explain or correct to improve consistency.

 

P4/P5 – An organizational matter, comment: The early paragraphs of the section 3. Results described experimental procedure details. Would these details not be better shifted to section 2 of the manuscript. In this reviewer’s view the Results section should describe the results and discuss salient features they imply with respect to the questions the manuscript aims to address.

 

P6 – L 200 and following: The author’s refer to precipitation of ‘eutectic phase’. This is incorrect terminology. The eutectic refers to a thermodynamic class or phase transformation involving formation of  at least two distinct solid phases from a liquid phase, i.e., a multi-phase equilibrium that involves an isotherm. Eutectic also refers to the solid microconstituent that forms from the liquid resulting from such an isothermal transformation. At minimum the word ‘phase’ in line 201 should be removed.

 

P7 – Table 3: There is systematic disagreement between the experimental results from DSC and also the cooling curve data analysis, which indicate an increase of the latent heat with an increase in the Cu concentration from 1 wt% to 4 wt%, and the predictions of the thermodynamic computer calculations via Thermo-Calc and JMatPro, which indicate the opposite trend, a decrease of the latent heat with increasing Cu concentration. THE MANUSCRIPT NARRATIVE needs to address this fundamental disagreement. The current narrative only describes quantitative differences between results obtained from experimentation and computation for each alloy composition in isolation without making any attempt to rationalize the diametrically opposite effects of Cu fraction on the thermophysical property of latent heat. Avoidance of this qualitative and fundamental discrepancy between experiments and computations renders the questionable the value of the presented discussion of the numerical differences of the latent heats obtained for the different alloy compositions. THIS is a major shortcoming, detracts from the quality and value of the contribution and must be remedied.

Author Response

Q1.P4 –L 132/133: Why stating AlSi7Cu1? Compositions in Table 1 all appear to indicate alloys of the tyoe Al5CuCux?  Explain or correct to improve consistency.

A1. You are right, there is a typing error at line 132. Instead of “AlSi5Cu(1, 2, 4) alloys,” it was written as “AlSi7Cu1 alloy.” This error will be corrected. The present sentence, “The experimental procedure involved one hypoeutectic AlSi7Cu1 alloy, the composition of which is listed in Table 1,” will be corrected to the following form: “The experimental procedure involved hypoeutectic AlSi5Cu(1, 2, 4) alloys, the composition of which is listed in Table 1.

Q2.P4/P5 – An organizational matter, comment: The early paragraphs of the section 3. Results described experimental procedure details. Would these details not be better shifted to section 2 of the manuscript. In this reviewer’s view the Results section should describe the results and discuss salient features they imply with respect to the questions the manuscript aims to address.

A2. Thank you for your valuable feedback and careful review of our manuscript. We appreciate your organizational suggestion regarding the placement of the experimental procedure details.

While we understand the rationale behind shifting these details to the "Materials and Methods" section, we have intentionally maintained our current structure. By placing a brief, preceding description of the experimental procedure at the start of the "Results" section, we provide essential context that enhances the reader's understanding. This approach creates a more cohesive narrative, allowing the reader to smoothly follow the process from how data was obtained to what the data revealed, without having to navigate back and forth between different sections. We believe this organization provides a clear and uninterrupted flow, making the findings easier to interpret. We are confident that this structure effectively supports our discussion and contributes to the overall clarity of the manuscript.

Q3. P6 – L 200 and following: The author’s refer to precipitation of ‘eutectic phase’. This is incorrect terminology. The eutectic refers to a thermodynamic class or phase transformation involving formation of  at least two distinct solid phases from a liquid phase, i.e., a multi-phase equilibrium that involves an isotherm. Eutectic also refers to the solid microconstituent that forms from the liquid resulting from such an isothermal transformation. At minimum the word ‘phase’ in line 201 should be removed.

A3. Thank you for your careful and detailed review. We appreciate your comment regarding our use of the term "eutectic phase" on line 200.

You are correct that, from a strict thermodynamic perspective, a eutectic is a phase transformation and the resulting microconstituent, not a single phase. We fully acknowledge this distinction. However, the term "eutectic phase" is commonly used in the metallurgical and materials science community to refer to the solidified eutectic constituent for simplicity and shortness, particularly in discussions of solidification paths and microstructures. This usage is found throughout peer reviewed literature and is intended to differentiate the eutectic constituent from the primary phase. Given this common practice in the field, we believe our current terminology is appropriate and helps to maintain the flow of the manuscript. However, we are happy to change the wording to "eutectic microconstituent" or "eutectic structure" if you feel it is necessary to improve the manuscript's clarity for a broader audience. Thank you again for your valuable input.

Q4. P7 – Table 3: There is systematic disagreement between the experimental results from DSC and also the cooling curve data analysis, which indicate an increase of the latent heat with an increase in the Cu concentration from 1 wt% to 4 wt%, and the predictions of the thermodynamic computer calculations via Thermo-Calc and JMatPro, which indicate the opposite trend, a decrease of the latent heat with increasing Cu concentration. THE MANUSCRIPT NARRATIVE needs to address this fundamental disagreement. The current narrative only describes quantitative differences between results obtained from experimentation and computation for each alloy composition in isolation without making any attempt to rationalize the diametrically opposite effects of Cu fraction on the thermophysical property of latent heat. Avoidance of this qualitative and fundamental discrepancy between experiments and computations renders the questionable the value of the presented discussion of the numerical differences of the latent heats obtained for the different alloy compositions. THIS is a major shortcoming, detracts from the quality and value of the contribution and must be remedied.

A4. Thank you for your worthy and sharp feedback. We completely agree with your assessment regarding the fundamental disagreement between our experimental results and the computational predictions from Thermo-Calc and JMatPro. You have accurately identified a major shortcoming in our current narrative, and we appreciate you bringing it to our attention. You are correct that our manuscript currently describes only quantitative differences without attempting to rationalize the diametrically opposite trends of latent heat with increasing copper concentration. This is a critical point that requires a comprehensive explanation.

We will revise the manuscript to include a new, dedicated discussion of this discrepancy, with the following rationale as a foundation for our argument:

• Non-equilibrium Solidification: Our experimental data, obtained via DSC and thermal analysis, represents a non-equilibrium solidification process. In contrast, Thermo-Calc and JMatPro are based on equilibrium thermodynamic calculations. The faster cooling rates in our experiments likely led to a different solidification path and the formation of non-equilibrium phases or microstructures.
• Complex Phase Formation: The higher copper concentration (up to 4 wt%) may have induced the formation of additional, kinetically driven phases that are not fully accounted for in the equilibrium models. The heat of precipitation for these phases could be a primary factor in the measured increase in latent heat.
• Model Limitations: While commercial software packages are powerful, their thermodynamic databases have inherent limitations and uncertainties, especially when applied to complex, multi component systems under non-equilibrium conditions. It is possible that the software's predictions for higher copper concentrations in this specific alloy system are limited compared to real world solidification behavior.

We will incorporate this discussion into providing deeper scientific context for our results, explicitly addressing the qualitative discrepancy you highlighted. This revision will significantly enhance the quality and value of our contribution. Thank you again for this crucial feedback, which will help us produce a more robust and scientifically sound manuscript.

Here is the added text related to this issue, which will be incorporated beneath line 338 in our manuscript:

The recognized disagreement between our experimental results and the computational predictions from Thermo-Calc and JMatPro, as presented in Table 3, requires a more detailed commentary. Specifically, our experimental data show an increase in latent heat with rising Cu concentration, while the computational predictions show the opposite trend. This "diametrically opposite effect" is a critical point that requires rationalization, as it highlights the limitations of equilibrium modeling when applied to real world solidification processes.

This deviation can be primarily attributed to the non-equilibrium nature of our experiments. While commercial software like Thermo-Calc and JMatPro perform calculations based on equilibrium phase diagrams, assuming infinitely slow cooling rates, our samples were subjected to controlled cooling, which is a non-equilibrium process. This faster cooling may lead to the formation of metastable phases or a different solidification path, where the precipitation of specific copper containing phases, such as the Al₂Cu phase, releases additional latent heat that is not fully captured by the equilibrium models.

Furthermore, the thermodynamic databases used in these software packages, while comprehensive, may not perfectly account for the complex interactions and kinetic effects that occur in multi-component systems like the AlSi₅Cu alloys. For instance, the formation and growth of the Al₂Cu phase may release a different amount of heat under non-equilibrium conditions than what is predicted at equilibrium. This qualitative discrepancy, therefore, highlights a crucial point: experimental analysis remains essential for understanding the true thermophysical behavior of alloys, particularly when complex kinetics are at play. This is a significant finding that adds substantial value to this study, providing a valuable point of reference for other researchers who rely on computational methods for predicting alloy behavior.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The present submission is a benchmarking of different methods for characterization of thermal properties of Al-Si-Cu alloys. However, comparison of standard DSC measurement with computer software (Thermo-Calc, JMatPro) calculation and Newtonian thermal analyses are reasonable there are some uncertainties for the reviewer and ask the authors for clarification.

Remelting and solidification procedure is described in the paper. Could the authors describe more accurately the experimental procedure and eventually publish a figure about the experimental setup. At least refer to a previous publication where they have presented it, please.

The authors refer to the paper (ref.24) for calculating the Cp based on the Kopp-Neumann rule. It is unclear for the reviewer if the Kopp-Neumann or the modified Kopp-Neumann were used in this paper. Please clarify.

Minor annotation foul in line 132, AlSi7Cu1 does not fit with table 1.

Additional Comment: The authors mention how important knowledge related to latent heat is for various alloy compositions for performing numerical simulation of solidification predicting properties and defect formation at casting. A detracting aspect of the whole efforts by the author is the missing comparison and connection the casting morphology. Pure date of latent heat is not enough to predict any important feature of the solidifying casting. The authors are encouraged to investigate alloy morphology and material properties to offer a more comprehensive characterization of the AlSiCu alloys.

Author Response

Q1. Remelting and solidification procedure is described in the paper. Could the authors describe more accurately the experimental procedure and eventually publish a figure about the experimental setup. At least refer to a previous publication where they have presented it, please.

A1. Thank you for your valuable feedback. We appreciate your request for a more detailed description of our experimental setup, as this is crucial for the reproducibility of our work. The remelting and solidification procedure, as well as the experimental setup, have been described in detail in our previous publication [please see references 1 and 15]. In brief, samples were melted in a resistance furnace under a protective argon atmosphere, with temperature monitored by a K-type thermocouple. Solidification was performed under controlled cooling within the furnace. We hope that this summary, along with the detailed reference, provides the necessary information for a complete understanding of our applied methodology.

Q2. The authors refer to the paper (ref.24) for calculating the Cp based on the Kopp-Neumann rule. It is unclear for the reviewer if the Kopp-Neumann or the modified Kopp-Neumann were used in this paper. Please clarify.

A2. We appreciate the reviewer's question. To clarify, in our paper we used the modified Kopp-Neumann rule as described and proposed in reference [24] to calculate the specific heat, Cp.

Q3. Minor annotation foul in line 132, AlSi7Cu1 does not fit with table 1.

A3. You are right, there is a typing error at line 132. Instead of “AlSi5Cu(1, 2, 4) alloys,” it was written as “AlSi7Cu1 alloy.” This error will be corrected. The present sentence, “The experimental procedure involved one hypoeutectic AlSi7Cu1 alloy, the composition of which is listed in Table 1,” will be corrected to the following form: “The experimental procedure involved hypoeutectic AlSi5Cu(1, 2, 4) alloys, the composition of which is listed in Table 1.

Q4. Additional Comment: The authors mention how important knowledge related to latent heat is for various alloy compositions for performing numerical simulation of solidification predicting properties and defect formation at casting. A detracting aspect of the whole efforts by the author is the missing comparison and connection the casting morphology. Pure date of latent heat is not enough to predict any important feature of the solidifying casting. The authors are encouraged to investigate alloy morphology and material properties to offer a more comprehensive characterization of the AlSiCu alloys.

A4. We appreciate the reviewer's valuable feedback and their intuitive comment regarding the connection between our thermophysical data and casting morphology. We fully agree that investigating the alloy morphology and material properties would offer a more comprehensive characterization. However, the primary objective of this manuscript is to provide a detailed and quantitative analysis of a fundamental thermophysical property latent heat and its relationship to alloy composition. Our work is intended to serve as a foundational study, providing crucial data that can be used by other researchers for numerical simulations and modeling of solidification, which can in turn be used to predict casting morphology and defect formation.

Adding a full investigation of morphology and material properties, while valuable, would significantly extend the scope of the current paper. We believe the present work is a complete and valuable contribution as a standalone study. We agree with the reviewer that this is a critical next step, and we plan to address this in future publication.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript evaluates the latent heat properties of AlSi5Cu (Cu = 1, 2, and 4 %) alloys using DSC, TA, and computational assessments with JMatPro and Thermo-Calc software packages. Different testing results are compared. To improve the manuscript, the following comments can be addressed.

1. The testing method of the latent heat can be reviewed in Introduction.

2. Why are the two commercial software packages used? If the prediction accuracy is the same, using a kind of software package is enough. Otherwise, which prediction result is acceptable?

3. What’s the zero curve? What’s the relation between Eq. (3) and Eq. (4)?

4. The Newtonian, Fourier, and Energy balance methods can be simply introduced.

5. Why is the DSC result used as the reference value?

6. Since the results using different methods are compared, which method is recommended to obtain more accuracy values? The authors can comment on it.

Author Response

Q1. The testing method of the latent heat can be reviewed in Introduction.

A1. Thank you for the constructive feedback. We have reviewed our manuscript and appreciate the suggestion to provide a more detailed description of the testing methods in the Introduction. However, we believe the current manuscript is structured to focus on the results and their implications. A comprehensive description of the methods for measuring latent heat, such as Differential Scanning Calorimetry (DSC) and thermal analysis, is widely available in the literature. Our reference list also includes several papers (e.g.1, 5., 6., 9., 14., 15, 16… ) that provide a detailed explanation of these well established techniques. To avoid redundancy and maintain the focused scope of the manuscript, we have chosen not to include a full review of these standard procedures. We believe that our current approach provides sufficient context for readers familiar with the field, while allowing us to dedicate more space to the unique findings of our study.

Q2. Why are the two commercial software packages used? If the prediction accuracy is the same, using a kind of software package is enough. Otherwise, which prediction result is acceptable?

A2. We appreciate the reviewer's question regarding the use of two commercial software packages. While Thermo-Calc and JMatPro are both powerful tools for thermodynamic calculations and share similar underlying principles, we chose to use both for a very specific reason: verification and validation.

By utilizing two independent software packages, each with its own specific thermodynamic database and computational approach, we were able to perform a cross validation of our results. Even with similar theoretical foundations, minor differences in their databases can lead to sensitive variations in the calculated values. The fact that the predictions from both software packages show the same qualitative trend (a decrease in latent heat with increasing Cu concentration), despite the quantitative differences with our experimental data, gives us a higher degree of confidence in their collective prediction.

This approach strengthens the scientific precision of our findings and adds to the credibility of our conclusions. Therefore, using both packages was not about seeking one "acceptable" result, but about confirming the robustness of the computational predictions and providing a more comprehensive comparison with our experimental data.

Q3. What’s the zero curve? What’s the relation between Eq. (3) and Eq. (4)?

A3. We thank the reviewer for their careful reading and for the opportunity to clarify these important points.

The "zero curve" (also known as the baseline or reference curve) represents the behavior of the investigated material during cooling when no phase changes occur. This ideal behavior is typical for amorphous materials or for single-phase cooling without any latent heat release. The purpose of the zero curve is to provide a baseline from which to measure the thermal effects of phase transformations. By subtracting this theoretical baseline from the actual cooling curve of the sample, we can isolate and quantify the thermal events (i.e., latent heat) associated with the solidification process.

Equations (3) and (4) are essentially linked, as they describe two different ways of calculating the same property the latent heat.

• Equation (3), which relates the change in temperature with the change in time (the first derivative), is used to calculate the area between the first derivative curve and the baseline. This area is a direct representation of the total heat released during solidification.
• Equation (4) takes the result from Equation (3) and converts it into a quantitative value for latent heat. It states that the latent heat, L, is calculated by multiplying the area under the first derivative curve (which is proportional to the heat released) by the average specific heat (Cp) of the alloy. This step is crucial because it translates the thermal signal measured by the analysis into a meaningful thermophysical property.

In essence, Equation (3) provides the raw data for the thermal event, while Equation (4) provides the method for converting that data into the specific latent heat value, thereby linking the thermal analysis signal to the material's properties.

Q4. The Newtonian, Fourier, and Energy balance methods can be simply introduced.

A4. Thank you for your valuable comment. We agree that a thorough understanding of the methods is crucial.

While we are familiar with all three methods: Newtonian, Fourier, and Energy Balance, and have employed them in our previous work, we used only the Newtonian method for this study. We chose this approach to maintain a consistent methodology with our current research and to streamline the focus of this manuscript. For a detailed description of all three methods, including the experimental setup and calculations, we kindly refer to the reviewer to our previous publications, specifically References [14] and [15] in our manuscript. We believe this approach provides the necessary information for the reader while keeping the current paper concise and focused on its primary objectives.

Q5. Why is the DSC result used as the reference value?

A5. Thank you for this sensitive question. We used the Differential Scanning Calorimetry (DSC) results as our reference value because DSC is a highly precise and widely accepted standard for measuring latent heat in materials. While thermal analysis is an effective method for in-situ measurements, DSC offers superior control over the cooling rate and has highly sensitive thermal sensors, making it the more accurate of the two experimental methods. Therefore, using the DSC data as our experimental benchmark allows for the most robust comparison against our computational models.

Q6. Since the results using different methods are compared, which method is recommended to obtain more accuracy values? The authors can comment on it.

A6. We appreciate the reviewer's question regarding the accuracy of the different methods. The choice of which method is most accurate depends entirely on the application and the conditions of the measurement. We can comment on this by classifying the methods into two main categories: laboratory based vs. foundry based.

• Laboratory Based Accuracy (DSC): For achieving the highest degree of accuracy in a controlled environment, Differential Scanning Calorimetry (DSC) is the recommended method. As noted in the manuscript, its precise temperature control and highly sensitive sensors make it the most reliable method for obtaining reference values. This is ideal for fundamental research and for generating data for thermodynamic databases.
• Foundry Based Accuracy (Thermal Analysis & Software): For practical, real world applications under industrial conditions (such as in a foundry), a combination of Thermal Analysis (TA) and commercial software packages is highly recommended. TA, while less precise than DSC, is a powerful and reliable on site tool for assessing the quality of a melt and for process control. The use of software packages like Thermo-Calc and JMatPro, despite their non-equilibrium limitations, provides a valuable predictive capability that allows engineers to anticipate solidification behavior and potential defects, especially when validated by experimental data.

In summary, while DSC provides the highest accuracy for a given measurement, TA and computational methods offer a level of accuracy that is entirely acceptable and, in fact, essential for industrial and predictive applications.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Regarding Q3 and A3 in the revised manuscript; The reviewer is fully aware of  the habits of the metallurgical field regarding the multiple implied meanings (context specific) and use of the phrase, ' eutectic'. Every manuscript added to the literature record offers an opportunity to enhance the correct use of technical and scientific terminology. As the authors recognize and acknowledge the actual misuse of the term 'eutectic phase', please, oblige and replace it as proposed in the response, I cite: "However, we are happy to change the wording to "eutectic microconstituent"or "eutectic structure" if you feel it is necessary to improve the manuscript's clarity for a broader audience. ".  

Remove or replace 'phase' as indicated above. 

The reviewer would like to thank the authors for the response to the queries. The revised manuscript addresses to reasonable level the concerns associated with the original manuscript after the required change of wording indicated above. 

 

Author Response

All the questions were answered and changes made in the manuscript accordingly. Figures quality improved, and autocitation issues solved.

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for your rectification, I accept it.

Author Response

All the questions were answered and changes made in the manuscript accordingly. Figures quality improved, and autocitation issues solved.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have addressed all comments, and this paper can be ready for publication.

Author Response

All the questions were answered and changes made in the manuscript accordingly. Figures quality improved, and autocitation issues solved.