Effect of Er on the Hot Deformation Behavior of the Crossover Al3Zn3Mg3Cu0.2Zr Alloy

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This work presents an okay work about the effect of Er on the hot deformation behavior of the crossover Al3Zn3Mg3Cu0.2Zr alloy. Some statements in the manuscript lack factual basis. A major revison is necessary before it can be considered for publication. The main concerns of the reviewer are

1. Lines 201-202 on page 6. How does the diffusion process determines the non-conservative movement of the dislocations? Could you provide some evidences about the variation of dislocation movement with temperature? 

2. Lines 204-205, the statement is unconvincing. Generally speaking, high strain rates lead to more significant dislocation nucleation and grain refinement driven by twinning and stacking fault, which is responsible for the higher stresses at high strain rates.

3. Lines 212-213, The statement is not consistent with Figs. 4 and 5. In Figs. 4 and 5, the addition of Er leads to decreases in true stress at the strain rates of 0.01/s, 0.1/s, and 1/s. If particle-stimulated nucleation softening mechanism is account for the decrease for strain rate of 0.01, what's the reason for the decreases for strain rates of 0.1 and 1.

4. Variables in formulas do not need to be defined repeatedly. For example, lines 229 on page 7 and 254 on page 8.

5. Line 259 on page 8. Could the evidences about variation of dislocation density with temperature be provided? As far as I know, atoms are more likely to slide and thus nucleate dislocations at high temperatures.

6. Line 264 on page 8. Could you provide some experimental observations about the decrease of the dislocation density caused by particle-stimulated nucleation dynamic recrystallization.

7. Line 182 on page 5, 'the grain size, size, and volume', please check it.

8. line 157 on page 6, 'The Er-rich alloy contain the', please check it.

Comments on the Quality of English Language

please see above 7 and 8.

Author Response

Dear Reviewer, thank you for your deep revision of our manuscript. We improve the manuscript in accordance to your comments. The changes were highlighted in yellow.

This work presents an okay work about the effect of Er on the hot deformation behavior of the crossover Al3Zn3Mg3Cu0.2Zr alloy. Some statements in the manuscript lack factual basis. A major revision is necessary before it can be considered for publication. The main concerns of the reviewer are

1. Lines 201-202 on page 6. How does the diffusion process determine the non-conservative movement of the dislocations? Could you provide some evidences about the variation of dislocation movement with temperature? 

Reply: Non-conservative movement of dislocations is movement not in the glide plane (climb). Such a movement movement needing the assistance of point defects (diffusion). The concentration of vacancies increases with increases of the temperature. As a result, the non-conservative velocity of dislocations increases.

2. Lines 204-205, the statement is unconvincing. Generally speaking, high strain rates lead to more significant dislocation nucleation and grain refinement driven by twinning and stacking fault, which is responsible for the higher stresses at high strain rates.

Reply: The twinning and stacking faults play insignificant role in the deformation process aluminum alloys at elevated temperatures even at high strain rates due too high stacking fault energy value.

3. Lines 212-213, The statement is not consistent with Figs. 4 and 5. In Figs. 4 and 5, the addition of Er leads to decreases in true stress at the strain rates of 0.01/s, 0.1/s, and 1/s. If particle-stimulated nucleation softening mechanism is account for the decrease for strain rate of 0.01, what's the reason for the decreases for strain rates of 0.1 and 1.

Reply: The reason of the decrease in stress at 0.1/s, and 1/s strain rates is the same as for 0.01/s (may be in a lower degree). The presence of micro-sized particles will introduce a large number of geometrically necessary dislocations to promote the occurrence of dynamic softening with particle-stimulated nucleation mechanism.

4. Variables in formulas do not need to be defined repeatedly. For example, lines 229 on page 7 and 254 on page 8.

Reply: The repeated variables after formula (6) were removed.

5. Line 259 on page 8. Could the evidences about variation of dislocation density with temperature be provided? As far as I know, atoms are more likely to slide and thus nucleate dislocations at high temperatures.

Reply: Indeed, the appearance of new dislocations from Frank–Read source may be faster at higher temperature. However, the annihilation of the dislocations is faster process. As a result, the dislocation density decreased with a rise of the temperature.

6. Line 264 on page 8. Could you provide some experimental observations about the decrease of the dislocation density caused by particle-stimulated nucleation dynamic recrystallization.

Reply: Unfortunately, the decrease of the dislocation density caused by particle-stimulated nucleation was not observed directly. However, indirect evidence as decreases of the stress may approve this fact.

7. Line 182 on page 5, 'the grain size, size, and volume', please check it.

Reply: Checked.

8. line 157 on page 6, 'The Er-rich alloy contain the', please check it.

Reply: Checked.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The paper considers the effect of addition of Er on mechanical behavior of an Al-Zn-Mg-Cu-Zr alloy at elevated temperatures. The experimental results are technically sound and deserve being presented to the scientific community, but the paper cannot be published in the present form. The English is insufficient. The text must be edited by a professional interpreter. A special attention should be paid to the use of the articles, prepositions, punctuation, the word “that”, the accordance between the subjects and the predicates.

 

Some sentences are difficult to read, if not impossible to understand, for example:

Lines 21-22. “The flow instability criteria for Er-doped alloy has a negative value”

Note that the criterion itself cannot have a sign. The criterion may mean that a specific expression is negative.

Lines 165-167. “An accompanying process during homogenization is heterogenization or decomposition of the supersaturated by zirconium or zirconium and erbium aluminum solid solution.”

Lines 206-207. “Before descent, two microstructural processes as strain hardening and dynamic recovery complete.”

Lines 207-208. “After the destination of the peak value dynamic recrystallization adds a contribution to the overall stress value.”

Lines 244-245. “The comparison of the experimental and predicted by the Eq. (3) true stress values, as well as.”

Lines 298-301. “The deformation of the Er-free alloy at strain rates higher than 0.1 s-1 may lead to the flow localization almost in the all temperature range at the beginning of deformation, which may provide the fracture at more hard deformation conditions than compression.”

 

Some sentences are unreasonably long and should be divided into parts, e.g., Lines 60-63: “A similar situation was observed in the as-forged Al-6.1Zn-2.1Mg-0.16Cu-0.15Zr-0.06Ti-0.06Fe-0.10Si [55] and as-cast Al-6.6Zn-1.7Mg-0.25Cu-0.15Zr [56] alloys, however, in the first case a value of effective activation energy is lower due to pre-deformed microstructure.”

The paragraph on the lines 165-180 is difficult to read because it presents a list of observations compiled without sufficient efforts to systematize or prioritize.

The portion of the text on the lines 189-189 of the section “Results and discussion” should appear in “Materials and methods”.

Moreover, the section “Results and discussion” is formatted as if it were a part of the “Materials and methods”.

If these issues are solved, the paper can be published. Concerning the essence of the paper, let me add one comment:

Lines 274-275: “The value of this coefficient is 0.17 for the Al3Zn3Mg3Cu alloy and 0.18 for the alloy with Er addition. “

The compared values are close to each other and only differ by 1 in the last significant digit. Is this difference significant? The error should be indicated.

Comments on the Quality of English Language

see the review

Author Response

Dear Reviewer, thank you for your deep revision of our manuscript. We improve the manuscript in accordance to your comments. The changes were highlighted in yellow.

 

Some sentences are difficult to read, if not impossible to understand, for example:

Lines 21-22. “The flow instability criteria for Er-doped alloy has a negative value”

Note that the criterion itself cannot have a sign. The criterion may mean that a specific expression is negative.

Reply: The sentence was rewritten.

 

Lines 165-167. “An accompanying process during homogenization is heterogenization or decomposition of the supersaturated by zirconium or zirconium and erbium aluminum solid solution.”

Reply: The sentence was rewritten.

An accompanying process during homogenization is heterogenization. The heterogenization is the decomposition of the supersaturated by zirconium or zirconium and erbium aluminum solid solution. The decomposition of the aluminum solid solution under annealing of the as-cast alloying following with L1₂ - Al₃M (M=Zr,Er) precipitates nucleation.

 

 

Lines 206-207. “Before descent, two microstructural processes as strain hardening and dynamic recovery complete.” Lines 207-208. “After the destination of the peak value dynamic recrystallization adds a contribution to the overall stress value.”

 

Reply: The sentences were rewritten.

Three main processes of the microstructure evaluation may proceed under hot deformation: strain hardening, dynamic recovery and dynamic recrystallization. The strain hardening and dynamic recovery took place before the reaching of the peak stress. The dynamic recrystallization is the main process under the decreasing of the stress.

 

 

Lines 244-245. “The comparison of the experimental and predicted by the Eq. (3) true stress values, as well as.”

Reply: The sentence was corrected.

The comparison of the experimental and predicted by the Eq. (3) true stress values, as well as constants of the constitutive equation are presented in Figure 6.

 

Lines 298-301. “The deformation of the Er-free alloy at strain rates higher than 0.1 s-1 may lead to the flow localization almost in the all temperature range at the beginning of deformation, which may provide the fracture at more hard deformation conditions than compression.”

 The sentences were rewritten.

Reply: The compression is one of the softest deformation process. However, using this we may construct the processing maps that show energy dissipation degree and flow localization. As shown in our investigation, the deformation of the Er-free alloy at strain rates higher than 0.1 s-1 may lead to the flow localization. Such a flow localization may provide the fracture at more hard deformation conditions than compression.

Some sentences are unreasonably long and should be divided into parts, e.g., Lines 60-63: “A similar situation was observed in the as-forged Al-6.1Zn-2.1Mg-0.16Cu-0.15Zr-0.06Ti-0.06Fe-0.10Si [55] and as-cast Al-6.6Zn-1.7Mg-0.25Cu-0.15Zr [56] alloys, however, in the first case a value of effective activation energy is lower due to pre-deformed microstructure.”

Reply: The sentence was corrected.

A lower value of the effective activation energy was obtained in the as-forged alloy [55] than in the as-cast alloy [56] alloy.

The paragraph on the lines 165-180 is difficult to read because it presents a list of observations compiled without sufficient efforts to systematize or prioritize.

Reply: The paragraph describes the effect of the Er on the precipitation behavior.

The paragraph contains:

• the introduction part:

“An accompanying process during homogenization is heterogenization. The heterogenization is the decomposition of the supersaturated by zirconium or zirconium and erbium aluminum solid solution. The decomposition of the aluminum solid solution under annealing of the as-cast alloying following with L1₂ - Al₃M (M=Zr,Er) precipitates nucleation.”

• The compared results of the SEM and TEM investigations:

 

“The measured EDX SEM content of the zirconium in the aluminum solid solution is 0.2-0.3%. The additional 0.3% of erbium was determined in the aluminum solid solution in the as-cast Al3Zn3Mg3CuEr alloy. The higher content of the precipitates forming elements in the Al3Zn3Mg3CuEr alloy must provide the higher volume fraction of the L1₂ precipitates. Erbium substitutes the zirconium atoms in the lattice of the L1₂-structured Al₃(Zr) precipitates [21-26, 30, 31]. The TEM microstructures of the alloys after solution treatment are presented in Fig.3. The Al3Zn3Mg3Cu alloy was solution treated at 480 °C for 3 h, and the Al3Zn3Mg3CuEr alloy - 480 °C for 3 h + 520 °C, 6 h. The L1₂-(Al₃Zr) precipitates with size of 40-100 nm were nucleated in the Er-free alloy (Fig.3a) after 3 h of solution treatment at 480 °C. The Fast Fourier Transformation (FFT) confirms the L1₂ structure of the precipitates (insert in the right image in Fig.3a).”

 

• The most important conclusion:

“Erbium addition in the alloy provides the formation of more stable and fine L1₂-(Al₃(Zr,Er)) precipitates after two-stage solution treatment with higher temperature of the second stage. The L1₂-(Al₃(Zr,Er)) precipitates have a size of 20-60 nm.”

The portion of the text on the lines 189-189 of the section “Results and discussion” should appear in “Materials and methods”.

Reply: As we noted in the Results and discussion part:

“The detailed investigation of the microstructure and phase composition of the as-cast and solution-treated Al3Zn3Mg3Cu and Al3Zn3Mg3CuEr alloys is presented in [34].”

We excluded from present manuscript methodology which was the main in the prevue paper [34]. We used some most important results with using reference:

“The solidus temperature determined by differential scanning calorimetry in [34] of the Al3Zn3Mg3Cu and Al3Zn3Mg3CuEr alloys is 493 and 477 °C respectively.”

Moreover, the section “Results and discussion” is formatted as if it were a part of the “Materials and methods”.

Reply: We agree that the part which describes the hot processing map creation can be presented as a part of the Materials and Methods. From the other hand, this part fits well to the Results and Discussion.

 

If these issues are solved, the paper can be published. Concerning the essence of the paper, let me add one comment:

Lines 274-275: “The value of this coefficient is 0.17 for the Al3Zn3Mg3Cu alloy and 0.18 for the alloy with Er addition. “

The compared values are close to each other and only differ by 1 in the last significant digit. Is this difference significant? The error should be indicated.

Reply: The error of the strain rate sensitivity coefficient was added. The difference between two coefficients is statistically significant.

 

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors investigated the effect of erbium alloying on the hot deformation behavior of the novel Al3Zn3Mg3Cu0.2Zr alloy. However, as mentioned in References [20-26], the early studies have discussed the influence of Er alloy element on the mechanical properties. The concept seems not to be novel. Thus, the title could be modified. Then, there are some improvements as follows:

1. In Abstract, it seems to be disorganized, so that man cannot catch the key problem in this study and their contribution.

2. In Introduction, the structure should be organized, such as, brief review of Al-Zn-Mg-Cu alloys, the influences of alloying elements, and then  the influences of under thermo-mechanical processing. Besides, References [20-26] should be discussed the influence of Er alloy element on the mechanical properties, so to state the problem that the authors would like to solve.

3. In Materials and methods, 2.3. Hot compression testing may be discussed before 2.2. Samples preparation and structure investigation. Hot compression testing was done firstly and then sample preparation and analysis.

4. In Section 3. Results and discussion, they can provide sub-sections, such as 3.1 Microstructure analysis of as cast and solution treatment, 3.2 Hot deformation behavior. In addition, Figure 8 is the key contribution of this study. Thus, they could discuss it in details. Otherwise, man cannot understand what is important of this figure. At the end the authors just point out three important points, but they don't explain them more in details.

5. The conclusions may be solid and focus on the issues of the hot deformation behavior, because the central concept of this study.   

  

Comments on the Quality of English Language

In Abstract, "Er increases the solidus 9 temperature of the alloy that provide increasing the hot deformation temperature" doen't have a period at the end. The authors should check the English again.

Author Response

Dear Reviewer, thank you for your deep revision of our manuscript. We improve the manuscript in accordance to your comments. The changes were highlighted in green.

 

The authors investigated the effect of erbium alloying on the hot deformation behavior of the novel Al3Zn3Mg3Cu0.2Zr alloy. However, as mentioned in References [20-26], the early studies have discussed the influence of Er alloy element on the mechanical properties. The concept seems not to be novel. Thus, the title could be modified.

Reply: We absolutely agree that the Er effect was investigated in [20-26]. The “novel” was applied to the alloy composition. The novel Al3Zn3Mg3Cu0.2Zr alloy with Er addition was presented in [34]. We modified the text and removed a “novel” word.

1. In Abstract, it seems to be disorganized, so that man cannot catch the key problem in this study and their contribution.

Reply: The main idea of the present manuscript is the demonstration of the significant effect of the Er alloying element to improving the hot deformation behavior of the crossover Al3Zn3Mg3Cu0.2Zr alloy.

The Er alloying provide three significant changes in the base alloy properties:

- increasing the solidus T;

- formation of the fine and thermally stable solidification origin phases;

- formation of the more stable and fine precipitates.

Indicated plusses provided by the better structure and hot deformation behavior.

The main results are indicated in the Abstract.

2. In Introduction, the structure should be organized, such as, brief review of Al-Zn-Mg-Cu alloys, the influences of alloying elements, and then  the influences of under thermo-mechanical processing. Besides, References [20-26] should be discussed the influence of Er alloy element on the mechanical properties, so to state the problem that the authors would like to solve.

Reply: The Introduction parts:

• The specific of the Al-Zn-Mg-Cu alloys:

“Wrought Al-Zn-Mg-Cu alloys are widely used in the aviation and aerospace in-dustries due to their high strength [1]. The highest content of alloying elements provides a great strengthening effect after aging treatment. The Zn/Mg ratio is more than 1 in the commercial Al-Zn-Mg-Cu alloys ensuring the high yield strength (YS), but the casting properties, heat, and corrosion resistance are low [1-6]. The Al-Zn-Mg-Cu alloys with a Zn/Mg ratio of 1 have medium strength, good castability, corrosion, and heat resistance [1,3-8].”

• The ways to improve the properties:

“The Al-Zn-Mg-Cu alloys with a Zn/Mg ratio of 1 have medium strength, good castability, corrosion, and heat resistance [1,3-8]. Another way to improve the casting properties is the alloying by eutectic forming elements [7-13]. Scandium and zirconium are well-known pair that may improve the room and elevated temperature mechanical properties of the Al-Zn-Mg-Cu alloys due to nucleation of nano-sized precipitates of L12-Al3(Sc,Zr) phase during solution treatment [14-21]. The similar effect on the microstructure and properties of Al may render the combination of Er and Zr [22-26].”

• Our vision of the alloying by Er:

“However, the Er is significantly cheaper than Sc. At the same time, Er may be not only a precipitate-forming element but also a eutectic-forming element [27-33]. Er-rich eutectic origin phases have an improved resistance to growth under high-temperature solution treatment that contributes to achieving a high strength of the alloy [27-33]. The novel cast and wrought Al-3Zn-3Mg-3Cu-Zr-Y(Er) alloy with improved heat resistance was developed based on these principles [34]. Developed alloys fit into the basic concept of the crossover alloys based on the using aluminum alloy scraps [35]. The crossover alloys cover the structure and properties of combined alloys of the different groups [36-44]. The developed Al-Zn-Mg-Cu-Zr-Y(Er) alloys took the best from the cast A-Zn-Mg alloys, high strength Al-Zn-Mg-Cu alloys, and heat resistant of the Al-Cu alloys [34, 44]. The presented features of the new alloys make them very prospective for deep investigations.”

• Hot deformation behavior of the Al-Zn-Mg-Cu alloys:

“The main way to improve the mechanical properties of the Al-Zn-Mg-Cu alloys is the control of grain structure under thermo-mechanical processing [14, 45-53]. Xu et. al. has shown that dynamic recovery is the main dynamic softening mechanism in the Al-5.6Zn-1.9Mg-0.3Cu-0.09Sc-0.09Zr alloy, at the same time, three dynamic recrystallization mechanisms (discontinuous, continuous and geometric) lead to grain refinement [54]. A lower value of the effective activation energy was obtained in the as-forged alloy [55] than in the as-cast alloy [56] alloy. Tang et. al. have investigated the influence of Zn content on the hot deformation behavior of Al-xZn-2Mg-2Cu alloys: the increase of Zn concentration from 6.3 to 10.1 % decreases the rate of dynamic recovery and dynamic recrystallization and decelerates dynamic softening [57]. However, the increase in Zn content does have not a significant influence on the static softening after hot deformation [58]. A Zr content has a more significant influence on static softening [59]. Elevated volume fraction of Al₃Zr dispersoids pinned dislocation and inhibited the dynamic recovery and/or recrystallization resulting in higher stored deformation energy in the hot deformed alloys. Consequently, more driving force for static softening is presented with increasing Zr additions. A similar influence of the hot deformation conditions (strain rate and temperature) on the post-deformation behavior was observed by Long et. al. [60]. The volume fraction of statically recrystallized grains is influenced by the stored deformation energy: at low deformation temperatures and high strain rates, the driving force for static recrystallization is higher. Hot deformation may influence also the phase composition of the alloys. Zhang et. al. has shown that hot rolling changes the morphology of Al₃Zr particles in 7055 aluminum alloy and leads to an increase in the dislocation density in subgrains and, consequently, results in an increased number and variety of quenching-induced phases [61].

At last time, the power tool for the investigation and modeling of hot deformation behavior called “processing mapping” was developed. This approach lets us determine optimal deformation conditions using minimum experimental data. This method was successfully applied for the 5A06 [62], 2195-O [63], ECO-7175 [64] aluminum alloys and TiC [65], CNT [66], and ZrB₂ [67] aluminum-based composites. ”

 

• The aim of the present investigation:

Reply: “The present investigation aims to determine the effect of Er alloying on parameters of the hot deformation of the Al-3Zn-3Mg-3Cu-0.2Zr under the modeling of the 3D-processing maps.”

Besides, References [20-26] should be discussed the influence of Er alloy element on the mechanical properties, so to state the problem that the authors would like to solve.

Reply: As we indicated the Authors of [20-26] used Er as only precipitates forming element. We present Er as not only a precipitate-forming element but also as a eutectic-forming element [27-33].

3. In Materials and methods, 2.3. Hot compression testing may be discussed before 2.2. Samples preparation and structure investigation. Hot compression testing was done firstly and then sample preparation and analysis.

Reply: We partially agree, but the grain structures (OM in fig.1), phase composition (SEM (fig.2) and TEM(fig.3)) were investigated before compression tests. The initial microstructure determines the hot deformation behavior. The grain structure evaluation after compression tests were investigated only.

 

4. In Section 3. Results and discussion, they can provide sub-sections, such as 3.1 Microstructure analysis of as cast and solution treatment, 3.2 Hot deformation behavior.

Reply: We divide the Results and discussion in sub-sections:

3.1. Microstructure analysis of as-cast and solution treated alloys

3.2. Hot deformation behavior

3.3. Hot processing maps

In addition, Figure 8 is the key contribution of this study. Thus, they could discuss it in details. Otherwise, man cannot understand what is important of this figure.

At the end the authors just point out three important points, but they don't explain them more in details.

Reply: We formulate these three main points based on all results and discussion illustrated before.

5. The conclusions may be solid and focus on the issues of the hot deformation behavior, because the central concept of this study.   

Reply: We agree that the hot deformation behavior is central concept of this study. However, the microstructure parameters have the main effect on the hot deformation behavior. We divide the conclusions on 6 points. The only one is not about the hot deformation behavior.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The revised manuscript can be considered for publication.

Author Response

Thank you for your time.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors answered to many of the questions raised in the first review and revised the English throughout the text. However,

-  Two of the questions need additional clarification (see below).

- Besides, the English still needs improvement. For example, the use of the word “that” should be revised, as its incorrect usage may mislead the reader. Also, the comment on “the accordance between the subjects and the predicates” was not addressed thoroughly. For example, line 305: “The second criteria that show instability”. Note that this is not the only place where such a problem occurs.

 

One of the questions concerned the expressions like “The flow instability criterion… has a negative value”. The comment in the first review said: “Note that the criterion itself cannot have a sign. The criterion may mean that a specific expression is negative.” The authors replaced the word “negative” with a sentence “less than zero”. This replacement with an equivalent expression does not answer to the comment. It is the strain rate sensitivity that becomes negative, not the criterion. In other words, the criterion of the flow instability is a negative value of the strain rate sensitivity.

 

The second question concerned the comparison of the values of 0.17 and 0.18. Now, the errors are indicated: 0.17±0.002 and 0.18±0.002. The error values justify the comparison. However, the expressions are not mathematically rigorous and do not respect the rules of presentation of data with errors. One of the basic rules is that the last significant figure in the result must correspond to the uncertainty, e.g., 0.177±0.002. The expressions should be completed accordingly.

Comments on the Quality of English Language

see the review

Author Response

The authors answered to many of the questions raised in the first review and revised the English throughout the text.

Reply: Dear Reviewer, thank you again for your help in improvement of our manuscript. We improve the manuscript in accordance to your last comments. The changes were highlighted in blue.

 

However,

-  Two of the questions need additional clarification (see below).

- Besides, the English still needs improvement. For example, the use of the word “that” should be revised, as its incorrect usage may mislead the reader. Also, the comment on “the accordance between the subjects and the predicates” was not addressed thoroughly. For example, line 305: “The second criteria that show instability”. Note that this is not the only place where such a problem occurs.

One of the questions concerned the expressions like “The flow instability criterion… has a negative value”. The comment in the first review said: “Note that the criterion itself cannot have a sign. The criterion may mean that a specific expression is negative.” The authors replaced the word “negative” with a sentence “less than zero”. This replacement with an equivalent expression does not answer to the comment. It is the strain rate sensitivity that becomes negative, not the criterion. In other words, the criterion of the flow instability is a negative value of the strain rate sensitivity.

Reply: The authors have polished English through the text and rephrased the sentences about flow instability criterion.

 

The second question concerned the comparison of the values of 0.17 and 0.18. Now, the errors are indicated: 0.17±0.002 and 0.18±0.002. The error values justify the comparison. However, the expressions are not mathematically rigorous and do not respect the rules of presentation of data with errors. One of the basic rules is that the last significant figure in the result must correspond to the uncertainty, e.g., 0.177±0.002. The expressions should be completed accordingly.

Reply: Yes, you are right. We have added the third digit after a dot. The values are still statistically different. The value of this coefficient is 0.174±0.002 for the Al3Zn3Mg3Cu alloy and 0.181±0.002 for the alloy with Er addition.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have revised the manuscript according to reviewer's comments. Now the quality seems to be good. I have not other comments.

Author Response

Thank you for your time.