Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper presents a significant and well-executed study on a promising new class of aluminum alloys. The work is characterized by a clear scientific rationale, rigorous experimentation, and novel findings that contribute meaningfully to the field of lightweight materials for high-temperature forming applications. The authors successfully demonstrate how compositional design, specifically the addition of Er and Cr, can tailor microstructure to achieve desirable superplastic properties. The paper is generally well-structured and the conclusions are supported by the data. I recommend publication after minor revisions to enhance its clarity, impact, and scholarly rigor.

1. While the presence of precipitates is well-documented, their direct role in stabilizing the fine-grained microstructure during superplastic deformation could be more quantitatively demonstrated. The current grain structure analysis in Figure 6 is from compression tests. It would be highly beneficial to include a similar micrograph (e.g., from OM or EBSD) of the gauge section of a tensile specimen after superplastic deformation (e.g., after >350% elongation). This would provide direct visual evidence of the retained equiaxed grains, conclusively proving the Zener pinning effect of the precipitates.
2. The discussion on activation energy (Q) is critical but currently spans two paragraphs in Section 3.3 and is somewhat repetitive. I recommend consolidating this discussion into a single, focused paragraph. Explicitly present the calculated Q-values for both alloys. Subsequently, interpret these values in the context of well-established diffusion mechanisms — for instance, grain boundary diffusion (~84 kJ/mol) and lattice diffusion (~142 kJ/mol). Finally, directly correlate this interpretation with the observed superplastic behavior. This will make the argument more concise and powerful.
3. The section on processing maps (Section 3.2) is informative but feels somewhat isolated from the main narrative on super-plasticity. To improve structural cohesion, consider adding a brief transitional sentence at the end of Section 3.2 or the beginning of Section 3.3. This sentence should explicitly state how the "safe" deformation domains identified in the processing maps (e.g., temperatures of 440-500°C) correlate with or provide a foundation for the optimal superplastic conditions (500-510°C) discovered later. This will create a stronger cause-and-effect narrative.
4. The phrase "does not have good superplastic properties" in the abstract could be replaced with the more specific "exhibits inferior superplastic properties."
5. While the difference in activation energy is provided, the underlying microstructural reason remains somewhat speculative. It is crucial to analyze the grain boundary character and precipitate distribution after superplastic deformationfor both alloys. EBSD analysis could reveal if Y-containing alloys have more pinned boundaries or less capacity for grain boundary sliding. TEM of post-deformed samples could show if Y-rich precipitates coarsen more rapidly, losing their Zener pinning effect.
6. The paper correctly notes that very low strain rates are industrially unattractive. To enhance the impact, the discussion should be expanded to more explicitly contextualize the best industrially relevant condition (1x10⁻³ s⁻¹, 510°C, >350% elongation). A brief comparison with the superplastic performance of well-known commercial alloys (e.g., AA5083, AA7475) at comparable strain rates would highlight the significance of the achieved results. Furthermore, a sentence or two speculating on potential thermo-mechanical processing routes to further increase the optimal superplastic strain rate would underscore the future potential of these alloys.

 

Comments for author File: Comments.pdf

Comments on the Quality of English Language

In summary, the English proficiency demonstrated in the manuscript is sufficient for peers and experts within the field to comprehend its core innovations and research findings. Prior to publication, it is strongly recommended to conduct a meticulous, line-by-line proofreading of the entire text, with particular attention given to correcting the spelling, grammatical, and formatting issues mentioned above. After this refinement process, the linguistic quality of the manuscript will be significantly enhanced, allowing it to be presented to the international academic community in a more professional manner.

Author Response

Dear Reviewer, thank you for working with our manuscript and provided comments. We improved the manuscript based on your comments. The changes were highlighted by yellow.

 

1. While the presence of precipitates is well-documented, their direct role in stabilizing the fine-grained microstructure during superplastic deformation could be more quantitatively demonstrated. The current grain structure analysis in Figure 6 is from compression tests. It would be highly beneficial to include a similar micrograph (e.g., from OM or EBSD) of the gauge section of a tensile specimen after superplastic deformation (e.g., after >350% elongation). This would provide direct visual evidence of the retained equiaxed grains, conclusively proving the Zener pinning effect of the precipitates.

 

 

Thank you very much for your comment, a Fig. 10 with the microstructure after failure in the temperature range of 480-520 ℃ and its description have been added to the text of the article:

 

After superplastic deformation, the grain size in the alloys increases, but equiaxed grains are preserved, indicating the significant role of the Zener pinning effect of the precipitates. The grain size in the alloy with Y is slightly larger than in the alloy with Er across the entire temperature range at a deformation rate of 1 × 10⁻³ s⁻¹. However, the residual porosity is significantly different, amounting to 5.5% and 1.4%, respectively, after deformation at the highest temperature of 520°C.

Fig. 10. Grain structure after superplastic deformation (failure) at temperatures of 480-520 °C and strain rate of 1 × 10⁻³ s⁻¹ of the Al2.5Zn2.5Mg2.5CuYCr  (a-c) and Al2.5Zn2.5Mg2.5CuErCr  (d-f) alloys (OM)

 

 

2. The discussion on activation energy (Q) is critical but currently spans two paragraphs in Section 3.3 and is somewhat repetitive. I recommend consolidating this discussion into a single, focused paragraph. Explicitly present the calculated Q-values for both alloys. Subsequently, interpret these values in the context of well-established diffusion mechanisms — for instance, grain boundary diffusion (~84 kJ/mol) and lattice diffusion (~142 kJ/mol). Finally, directly correlate this interpretation with the observed superplastic behavior. This will make the argument more concise and powerful.

 

 

Thank you. The text of the article has been changed in accordance with the comment:

 “The data of the linear region II (Fig. 8) were used not only to estimate the stress exponent but also the effective activation energy of superplastic deformation. The strain rate-sensitivity index m is an indirect method for assessing the mechanisms of superplastic deformation. The main contributions are believed to come from grain boundary sliding m = 0.5, dislocation climb m =0.2-0.3, and diffusion creep m = 1. The combination of these independent mechanisms also provides a value of m close to 0.5. In both alloys, m-values ​​are 0.6-0.8, indicating a low contribution from the dislocation component. However, it is difficult to determine which mechanism is dominant based on the m-values. Therefore, calculation of the effective activation energy is preferred, which allows one to determine the contribution of the main mechanism of superplastic deformation. It is known that during superplastic deformation, the values ​​of main mechanism and Q can be changed. For the calculation, a strain rate of 1 × 10⁻³ s⁻¹ was chosen, which corresponds to region II of deformation. At the initial strain, it is difficult to determine the main deformation mechanism, as there is a strong increase in stress due to microstructural changes. Accordingly, the effective activation energy was calculated at a strain greater than 100% (the steady deformation stage), when there is no change in stress for both alloys. Effective activation energy is calculated using the equation (1). It is known from the literature that the most informative and least error-prone method is the calculation of the activation energy using the equation (2) using the hyperbolic sine. The effective activation energy determined by this equation (2) is a critical parameter for determining the level of complexity for possible superplastic deformation of materials at high temperatures. In the Al2.5Zn2.5Mg2.5CuErCr alloy, the activation energy is ~128±10 kJ/mol, while in the Al2.5Zn2.5Mg2.5CuYCr alloy, it is ~220±17 kJ/mol. During superplastic deformation of aluminum alloys, if the Q value is 84 kJ/mol [70-72], the process is controlled by grain boundary diffusion, i.e., grain boundary sliding. If the Q value is near lattice diffusion ~142 kJ/mol [70-72], then the deformation is controlled by self-diffusion of pure aluminum. The Q in alloy with Er lies between the grain boundary and lattice self-diffusion activation energy of pure Al [72,73]. The results show that there are both grain boundary self-diffusion and lattice self-diffusion during deformation in Er-doped alloy. Whereas in the Y-doped alloy the value of Q is high and predominant mechanism that controlled the superplastic flow is diffusion creep. High values can be explained by the influence of alloying elements and second-phase particles on the diffusion characteristics of the alloy. Diffusion creep is a slow process, which limits the strain rate and possibility of superplastic deformation. After annealing, equiaxed grains were observed in both alloys due to the PSN effect of the coarse particles, which facilitate dynamic recrystallization. However, a comparison of the behavior during superplastic deformation and the effective activation energy suggests that the second-phase particles and/or the excessively dissolved element Y had a strong influence on the recrystallization behavior, slowing grain boundary sliding. Diffusion creep occurs simultaneously with grain boundary sliding in the Al2.5Zn2.5Mg2.5CuErCr alloy. The deformation process is accompanied by sliding of the adjacent grains along grain boundaries, grain rotation and grain neighbour switching. Due to better accommodation and the action of two deformation mechanisms, the Al2.5Zn2.5Mg2.5CuErCr alloy has lower residual porosity and lower stress during deformation, which is also associated with a smaller grain size. The elongation of the grains along the tensile axis, usually associated with Lifshitz sliding, occurs due to the diffusion creep mechanism, which is consistent with the grain size; in the Al2.5Zn2.5Mg2.5CuYCr alloy, it is larger.”

 

 

 

3. The section on processing maps (Section 3.2) is informative but feels somewhat isolated from the main narrative on super-plasticity. To improve structural cohesion, consider adding a brief transitional sentence at the end of Section 3.2 or the beginning of Section 3.3. This sentence should explicitly state how the "safe" deformation domains identified in the processing maps (e.g., temperatures of 440-500°C) correlate with or provide a foundation for the optimal superplastic conditions (500-510°C) discovered later. This will create a stronger cause-and-effect narrative.

 

The processing maps were constructed for strain rates of 10^-2-10 s^-1. The superplasticity was investigated for strain rates of 10^-4-10^-3 s^-1. Two these parts (3.2 and 3.3) were not connected as one follow from another one. Two these parts are overlapping large range of deformation rates which are usual for conventional thermo-mechanical treatment (high strain rates) and suprerplasticity forging (low strain rates).

 

4. The phrase "does not have good superplastic properties" in the abstract could be replaced with the more specific "exhibits inferior superplastic properties."

 

Thank you. It was revised.

 

5. While the difference in activation energy is provided, the underlying microstructural reason remains somewhat speculative. It is crucial to analyze the grain boundary character and precipitate distribution after superplastic deformation for both alloys. EBSD analysis could reveal if Y-containing alloys have more pinned boundaries or less capacity for grain boundary sliding. TEM of post-deformed samples could show if Y-rich precipitates coarsen more rapidly, losing their Zener pinning effect.

 

We absolutely agree. The deep investigation of the superplasticity mechanisms and precipitates evaluation is very important and will be aim of our future manuscript. The present manuscript was mainly aimed to demonstrate the deformation behavior of novel Al alloy in wide range of strain ranges.

 

6. The paper correctly notes that very low strain rates are industrially unattractive. To enhance the impact, the discussion should be expanded to more explicitly contextualize the best industrially relevant condition (1x10⁻³ s⁻¹, 510°C, >350% elongation). A brief comparison with the superplastic performance of well-known commercial alloys (e.g., AA5083, AA7475) at comparable strain rates would highlight the significance of the achieved results. Furthermore, a sentence or two speculating on potential thermo-mechanical processing routes to further increase the optimal superplastic strain rate would underscore the future potential of these alloys.

 

Thank you for your comment. We have supplemented the comparison with industrial alloys and suggested thermomechanical treatment to improve the properties.

“The developed and studied Er-doped alloy is promising for industrial use in super-plastic forming, as it exhibits sufficient elongations (>350%) at 510 °C and a strain rate of 1 × 10−3 s−1. For industrial applications, deformation at lower temperatures and higher strain rates is preferable. The AA5083 and AA7475 alloys used in industry are deformed at sub-solidus temperatures (500-550 ℃) and at a strain rate of 1 × 10−3 s−1, but the maximum elongation is near 300% with same thermomechanical treatment [74-75]. Increasing the strain rate is preferable than decreasing the temperature. Therefore, grain size reduction in the Al2.5Zn2.5Mg2.5CuErCr and Al2.5Zn2.5Mg2.5CuYCr alloys can be achieved using multi-directional isothermal forging, as a promising method for grain refinement and in-creasing superplastic properties (with a smaller grain size, it is possible to change the temperature-strain rate regime).”

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript reports an experimental investigation of precipitation behavior, hot deformation, and superplastic properties of two crossover aluminum alloys: one containing Y and one containing Er. The topic is important and fits well within the journal’s scope, particularly due to the increasing industrial interest in low-cost superplastic alloys and crossover alloying strategies. The manuscript presents TEM characterization, hot compression testing, tensile superplasticity assessments, activation energy analysis, and processing maps. However, despite the technical relevance, the manuscript requires substantial scientific, structural, and linguistic revisions before it can be considered for publication. Below are detailed suggestions for enhancing the clarity, impact, and overall quality of the manuscript.

• Can the authors clearly explain what is new in this study compared to their previously published works on similar Y/Er-containing crossover alloys (e.g., refs. 32–34)?
• What specific scientific gap does this manuscript fill that is not already addressed in earlier publications by the same group?
• How does the present work advance knowledge beyond existing literature on superplastic crossover alloys?
• Why was a double-step solution treatment (480°C + 520°C) used, and how were these temperatures selected?
• Can the authors provide complete rolling details (reductions, number of passes, interpass temperatures, lubrication, reheating sequence)?
• How was temperature uniformity ensured during high-temperature tensile tests?
• How many specimens were tested for each condition, and what were the standard deviations of the results?
• What was the method for grain size measurement (standard, number of fields, number of grains counted)?
• How were TEM samples selected to ensure statistical significance and representativeness?
• Can the authors provide indexed SAED/FFT patterns to confirm the D₀₂₃, E-phase, and quasicrystalline structures?
• Can the authors supply TEM-EDS data showing the chemical composition of each precipitate type?
• What is the number density, volume fraction, and size distribution of the D₀₂₃ and E-phase precipitates?
• What evidence confirms that some precipitates are truly quasicrystalline rather than partially ordered regions?
• How do the authors believe QC precipitates influence grain growth and superplasticity?
• Why was activation energy (Q) calculated at 100% strain rather than specifically in Region II of the sigmoidal curve?
• Can the authors clarify whether grain boundary sliding, lattice diffusion, or dislocation creep dominates superplastic deformation in each alloy?
• Can they compare Q values more rigorously with known diffusion values for Al, Al-alloys, and related systems?
• Why do microstructures after hot compression (Fig. 6) not show DRX despite claims of recrystallization?
• How do the processing maps correlate with the tensile superplastic behavior?
• What are the grain sizes after superplastic deformation at 500–510°C?
• Why does the Y-containing alloy not show superplasticity despite similar grain sizes?
• How does the performance compare with known superplastic alloys (e.g., AA5083, AA7475, SPC alloys)?
• Can the authors expand on how Cr addition influences E-phase formation and thermal stability?
• Can they further compare their results to the Acta Materialia 2023 crossover alloy (ref. 49)?
• How does the non-equiaxed grain shape in the Er-alloy affect superplasticity?
• Why does grain elongation occur more strongly in the Er-containing alloy?
• While the manuscript is generally well-written, there are areas where sentence structure could be improved for clarity. Thus, proofreading is necessary to correct major grammatical errors and to streamline complex sentences would improve readability.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

While the manuscript is generally well-written, there are areas where sentence structure could be improved for clarity. Thus, proofreading is necessary to correct major grammatical errors and to streamline complex sentences would improve readability.

Author Response

Dear Reviewer, thank you for working with our manuscript and provided comments. We improved the manuscript based on your comments. The changes were highlighted by turquoise.

 

1. Can the authors clearly explain what is new in this study compared to their previously published works on similar Y/Er-containing crossover alloys (e.g., refs. 32–34)?

 

All data in this paper are new and not be presented in prevue manuscripts. The microstructure and phase composition (OM and SEM), homogenization process, aging process in the alloys presented in this study were investigated in [33]. The refs [32, 34] presented another alloys (without Cr and with 3% of Zn/Mg/Cu). The as-rolled structure, TEM investigation, deformation behavior, superplasticity were investigated firstly in the presented manuscript.

 

2. What specific scientific gap does this manuscript fill that is not already addressed in earlier publications by the same group?

 

First of all, we developed novel alloys [33]. The main principles of the alloys creation were presented in [33]. The drafted manuscript explain the precipitation behavior of novel alloys and deformation behavior in wide range of deformation rates which are usual for conventional thermo-mechanical treatment (high strain rates) and suprerplasticity forging (low strain rates).

 

3. How does the present work advance knowledge beyond existing literature on superplastic crossover alloys?

The crossover alloys of Al-Zn-Mg-Cu system are still typical wrought alloys with structure mainly consisted from Al solid solution, see, for example, [49]. The eutectic forming elements, such as Ni and Fe, are usually added to Al-Zn-Mg-Cu alloys to provide dynamic recrystallization under superplasticity. The role of eutectic forming elements in our new alloys played Y/Er with Cu, at the same time, the Y/Er with Zr are the precipitates forming elements. As a result, the Y/Er have the major role in the superplasticity of the new alloys: they provide dynamic recovery and pinning grain growth through the formation of fine eutectic phases and fine precipitates.

 

4. Why was a double-step solution treatment (480°C + 520°C) used, and how were these temperatures selected?

 

The regime of solution treatment was developed and explained in details in [33]. Please see this manuscript. We did not include this information to avoid repetition.

 

5. Can the authors provide complete rolling details (reductions, number of passes, interpass temperatures, lubrication, reheating sequence)?

 

The information about rolling is in the [33]:

“Following solution treatment at 480–520 ◦C and water quenching, the ingot underwent hot rolling at 500 ◦C, starting from a thickness of 20 mm to 5 mm and, at room temperature, to 1 mm thickness sheets”

Additionally, the thickness reduction under hot deformation was about 1 mm per pass, the sample was back to furnace after 3 passes. The reduction under cold rolling was about 0.5 mm per pass.

We did not include this information to avoid repetition.

 

6. How was temperature uniformity ensured during high-temperature tensile tests?

The thermocouple was welded to the sample under compression tests. The heating was provided by current.

The superplasticity tests were did in the resistance furnace with three controlling thermocouples.

 

7. How many specimens were tested for each condition, and what were the standard deviations of the results?

16 samples were used to construction processing maps. The test was repeated if the results were not lie in the predicted results. This is possible if only sample have significant defects after cast.

The data about superplacticity were collected from many experiments at different temperatures and strain rates with obtained of tradition dependencies (Fig.8-9).

 

8. What was the method for grain size measurement (standard, number of fields, number of grains counted)?

The grain size was measured by secant method based on three images for each state. The typical images are presented in Fig. 7.

 

9. How were TEM samples selected to ensure statistical significance and representativeness?

The rolling with high deformation including cold rolling from 5 to 1 mm provides very uniform microstructure in whole sheet. It can be confirmed by many results of tensile tests of samples cutter from different parts of sheet, uniformity of structure investigated by SEM and etc.

 

10. Can the authors provide indexed SAED/FFT patterns to confirm the D₀₂₃, E-phase, and quasicrystalline structures? 11. Can the authors supply TEM-EDS data showing the chemical composition of each precipitate type?

 

The typical reflexes are labeled, the orientation of Al matrix is added to each FFT. The D₀₂₃ and E-phases were very deep investigated by many researchers. We used references to confirm it. We presented enough information to prove obtained data. The quasicrystall is phase with long-range orientation order and without translation symmetry. It is mean that the reflexes have not indexes. Please see D. Shechtman and colleagues [53]. The resolution of our TEM-EDS is not enough to determine the chemical composition of so fine precipitates, unfortunately.

 

12. What is the number density, volume fraction, and size distribution of the D₀₂₃ and E-phase precipitates?

We may use the calculated values of volume fraction obtained in [33]. We have not enough data to measure the real volume fraction. We added the confidence value to diameter of D₀₂₃-precipiates. The range of E precipitates length is indicated. The concrete quantitative values are not sufficient to the present study. The detailed deep analyzes will provided in future work under investigation of the superplasticity mechanisms in the novel alloys.

 

13. What evidence confirms that some precipitates are truly quasicrystalline rather than partially ordered regions?

The not labeled reflexes in Fig.2e repeated typical FFT (SAED) from quasicrystal, please see [53] and FFT in image f. The obtained FFT is constructed from one precipitate in which can be divided to types of structures.

 

14. How do the authors believe QC precipitates influence grain growth and superplasticity?

The QC precipitates were found as separate single precipitates in large volume. The fraction of precipitates with QC structure is incomparable low. While we not divided E with crystal and QC structure.

 

15 Why was activation energy (Q) calculated at 100% strain rather than specifically in Region II of the sigmoidal curve?

 

Thank you for your comment. We have supplemented the explanations.

«The strain rate-sensitivity index m is an indirect method for assessing the mechanisms of superplastic deformation. The main contributions are believed to come from grain boundary sliding m = 0.5, dislocation climb m =0.2-0.3, and diffusion creep m = 1. The combination of these independent mechanisms also provides a value of m close to 0.5. In both alloys, m-values are 0.6-0.8, indicating a low contribution from the dislocation component. However, it is difficult to determine which mechanism is dominant based on the m-values. Therefore, calculation of the effective activation energy is preferred, which allows one to determine the contribution of the main mechanism of superplastic deformation. It is known that during superplastic deformation, the values of main mechanism and Q can be changed. For the calculation, a strain rate of 1 × 10−3 s−1 was chosen, which corresponds to region II of deformation. At the initial strain, it is difficult to determine the main deformation mechanism, as there is a strong increase in stress due to microstructural changes. Accordingly, the effective activation energy was calculated at a strain greater than 100% (the steady deformation stage), when there is no change in stress for both alloys.»

 

16 Can the authors clarify whether grain boundary sliding, lattice diffusion, or dislocation creep dominates superplastic deformation in each alloy?

 

Thank you. We've clarified the influence of the acing mechanisms during superplastic deformation and rewritten the paragraph on the effective activation energy of the deformation process.

 

17 Can they compare Q values more rigorously with known diffusion values for Al, Al-alloys, and related systems?

 

Thanks for the comment. We've made a comparison.

Activation energy values ​​for industrial alloys vary depending on their composition. For example, for AA5083, it is around 200 kJ/mol [75], while in high-strength alloys (AA7475), it is around 112 kJ/mol [74]l, that indicating the presence of different deformation mechanisms. Presumably, the AA5083 alloy and AA7475 exhibit high values ​​relative to the self-diffusion of pure aluminum, due to the distortion of the crystal lattice during the formation of the solid solution and the presence of dispersed particles with a size of approximately 40 nm. Low Q values ​​are not found in industrial alloys, but are possible in alloys with a non-recrystallized microstructure prior to fracture.

 

 

18 Why do microstructures after hot compression (Fig. 6) not show DRX despite claims of recrystallization?

The high strain rates under compression do not provide dynamic recrystallization as was demonstrated by calculation and structure analyzes. Under lower strain rates at superplacticity tests the DRX is processed.

 

19 How do the processing maps correlate with the tensile superplastic behavior?

The processing maps were constructed for strain rates of 10^-2-10 s^-1. The superplasticity was investigated for strain rates of 10^-4-10^-3 s^-1. Two these parts (3.2 and 3.3) were not connected as one follow from another one. Two these parts are overlapping large range of deformation rates which are usual for conventional thermo-mechanical treatment (high strain rates) and suprerplasticity forging (low strain rates).

 

20 What are the grain sizes after superplastic deformation at 500–510°C?

 

The text of the article has been corrected.

The microstructure of alloys after superplastic deformation at a rate of 1 × 10−3 s−1 in the temperature range of 480-520°C was studied (Fig. 10). After deformation at lower temperatures, for example, 480°C, the grain size in the alloy with Y is 15,3 ± 1,6 μm, while in the alloy with Er it is 12,0 ± 1,2 μm. With increasing temperature, the grain size increases and in the range of 500-510 °C it is 12,7 ±  1,4 μm and 11,3 ± 1,5 μm in the alloy with Y and Er, respectively. At a subsolidus temperature of 520°C, the grain sizes are 15,6 ± 2,4 µm and 12,7 ± 1,3 µm, respectively. However, it is worth noting the high proportion of residual porosity in the Al2.5Zn2.5Mg2.5CuYCr.

 

21 Why does the Y-containing alloy not show superplasticity despite similar grain sizes?

TEM investigations of post-deformed samples could show differences in Y-rich precipitates. The deep investigation of the superplasticity mechanisms and precipitates evaluation is very important and will be aim of our future manuscript. The present manuscript was mainly aimed to demonstrate the deformation behavior of novel Al alloy in wide range of strain ranges.

 

 

22 How does the performance compare with known superplastic alloys (e.g., AA5083, AA7475, SPC alloys)?

The text of the article has been supplemented:

«Activation energy values ​​for industrial alloys vary depending on their composition. For example, for AA5083, it is around 200 kJ/mol [75], while in high-strength alloys (AA7475), it is around 112 kJ/mol [74]l, that indicating the presence of different deformation mechanisms.

…

The AA5083 and AA7475 alloys used in industry are deformed at subsolidus temperatures (500-550 ℃) and at a strain rate of 1 × 10⁻³ s⁻¹, but the maximum elongation is near 300% with same thermomechanical treatment [74-75].»

 

 

23 Can the authors expand on how Cr addition influences E-phase formation and thermal stability?

 

Chromium is well-known precipitates forming element in Al alloys. The formation of Al7Cr or E(Al₁₈Mg₃Cr₂) is typical and investigated by many researchers. The fine precipitates are effectively pinning the dislocation movement what provide high strength at room and elevated temperatures.

 

24 Can they further compare their results to the Acta Materialia 2023 crossover alloy (ref. 49)?

 

The unusual Al-4.91Mg-3.46Zn-0.46Cu-0.33Mn-Cr-Fe-Si crossover alloy was investigated in the [49]. The typical structure for achieving good superplasticity was provided by micron sized T phase and E(Al₁₈Mg₃Cr₂) precipitates. Similar elongation was achieved in the Al-4.91Mg-3.46Zn-0.46Cu-0.33Mn-Cr-Fe-Si crossover alloy in the wide range of strain rates of 10⁻² s⁻¹ or 5·10⁻⁵ s^–1.

 

25 How does the non-equiaxed grain shape in the Er-alloy affect superplasticity?

 

In both alloys, recrystallization occurs during superplastic deformation, and the grains elongate along the deformation direction. Grain size has a greater effect on superplastic deformation than elongation. In the Y-doped alloy, the grain is more elongated due to the greater contribution of diffusion creep, while in the Er-doped alloy, it is less. A smaller grain size allows for better superplastic properties. The text of the article has been corrected.

 

26 Why does grain elongation occur more strongly in the Er-containing alloy?

 

The grain size in the Al2.5Zn2.5Mg2.5CuYCr alloy is larger than in the Al2.5Zn2.5Mg2.5CuErCr alloy due to the smaller PSN effect of the coarse particles, which facilitate dynamic recrystallization.

 

27 While the manuscript is generally well-written, there are areas where sentence structure could be 28 improved for clarity. Thus, proofreading is necessary to correct major grammatical errors and to streamline complex sentences would improve readability.

 

The manuscript was carefully checked and revised.

 

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors

First of all, I congratulate the Authors on an interesting article. However, I have a few minor comments aimed at improving it:

• In the abstract, I suggest adding (emphasizing) the main purpose of the work.
• In the introduction, which is a literature review, I suggest avoiding citations to [6-22] (as done in line 33).
• Please standardize the notation: Al-2.5Zn-2.5Mg-2.5Cu-Er(Y)-Zr-Ti-Fe-Si. The title and text are different. - In my opinion, Table 1 should be placed in section 2, where the material used for the research is described.
• The graphs presented in Figure 3 are difficult to see. Additionally, please explain why two graphs with the results are provided for, for example, different strain rates of 0.01 s-1 (a, b) and the remaining different strain rates of 0.1 s-1 (c, d), 1 s-1 (e, f), and 10 s-1 (g, h). What does this contribute to the work?
• Fig. 8 presents the results without specifying the parameters they refer to in the legend. The lines are solid and dashed. Please explain and comment.
• In the summary, I propose to additionally address the achievement of the work's stated goal.

Author Response

Dear Reviewer, thank you for working with our manuscript and provided comments. We improved the manuscript based on your comments. The changes were highlighted by green.

 

 

1. In the abstract, I suggest adding (emphasizing) the main purpose of the work.

In the introduction, which is a literature review, I suggest avoiding citations to [6-22] (as done in line 33).

 

The aim was added. The sentence with wide range of references was revised.

 

2. Please standardize the notation: Al-2.5Zn-2.5Mg-2.5Cu-Er(Y)-Zr-Ti-Fe-Si. The title and text are different. - In my opinion, Table 1 should be placed in section 2, where the material used for the research is described.

 

The alloys compositions and abbreviations were revised. The Table 1 was replaced in part 2.

 

3. The graphs presented in Figure 3 are difficult to see. Additionally, please explain why two graphs with the results are provided for, for example, different strain rates of 0.01 s-1 (a, b) and the remaining different strain rates of 0.1 s-1 (c, d), 1 s-1 (e, f), and 10 s-1 (g, h). What does this contribute to the work?

 

The graphs were revised to the best visualization.

The compression curves for both alloys are presented - (a,c,e,g) Al2.5Zn2.5Mg2.5CuYCr and (b,d,f,h) Al2.5Zn2.5Mg2.5CuErCr alloys.

Left line of images  (a,c,e,g) is for alloy with Y and right (b,d,f,h) line - for alloy with Er. We have two graphs to each strain rate.

 

4. Fig. 8 presents the results without specifying the parameters they refer to in the legend. The lines are solid and dashed. Please explain and comment.

 

Thank you very much for your comment. The Fig. 8 was revised. We've corrected the legend and caption.

 

Fig.8. The stress–strain rate behavior and the strain rate sensitivity m-coefficient vs strain rate for alloys (a) Al2.5Zn2.5Mg2.5CuYCr and (b) Al2.5Zn2.5Mg2.5CuErCr (solid lines refer to the flow stress σ, dashed lines - to the coefficient m) 

 

5. In the summary, I propose to additionally address the achievement of the work's stated goal.

 The summary was revised.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The current form of the manuscript is accepted for publication. The authors have addressed all my comments and made a significant contribution to the field, and their findings will significantly interest the readers of Journal of Manufacturing and Materials Processing.