Investigation of the Effect of Heat Treatment on the Microstructures and Mechanical Properties of Al-13Si-5Cu-2Ni Alloy

Round 1

Reviewer 1 Report

Dear Autors
The article is written correctly. Everything is presented in a readable way for the reader. The basics of the research were presented. Conditions for obtaining alloys. The treatment applied to the tested materials is then shown. Research and results are described and conclusions are presented. The only thing that could be added is to present the geometry of the tested samples (maybe a photo or drawing) and the number of samples tested for individual alloys. For example, the number of hardness measurements performed for one sample is given, but I have not found how many samples of a given type are tested.
However, this does not affect the overall value of the article.

Kind regards,

Reviewer

Author Response

Response to the reviewer’s comments

Thank you for your comments. They are very insightful and constructive to improve our manuscript. We have carefully revised the manuscript according to the comments. The following is a point-to-point response to your comments.

Reviewer's comments:

Reviewer #1:

1. The only thing that could be added is to present the geometry of the tested samples (maybe a photo or drawing). For example, the number of hardness measurements performed for one sample is given, but I have not found how many samples of a given type are tested.

 

Reply:

We thank the reviewer very much for the encouraging comments and recognition of our work. It is necessary to show the geometry of the test samples. In this work, eight samples (aging treated for from 0 to 14h at 165 °C) were tested microhardness, and one single sample was tested by 10 points and removing the maximum and minimum values to calculate the mean values for the Vickers hardness. The geometry of the tensile test samples is as follows:

See in Lines 128-130 on Page 3:

Figure 1. Dimensions of tensile sample

See in Lines 118-121 on Page 3:

And eight samples (aging treated for from 0 to 14h at 165 °C) were tested microhardness. Mean values for the Vickers hardness were obtained by testing 10 points on a single sample and removing the maximum and minimum values.

 

 

2. The thing that could be added is to present the number of samples tested for individual alloys. For example, the number of hardness measurements performed for one sample is given, but I have not found how many samples of a given type are tested.

 

Reply:

  Thank you very much for your professional comments. we have further improved this paper according to your comments and revised our manuscript, as follow:

 

See in Lines 116-121 on Page 3:

  At least three tensile samples were tested. The microhardness of each sample was measured using a Vickers hardness tester, with an applied load of 50 N and a duration of 10 s. Mean values for the Vickers hardness were obtained by testing 10 points on one single sample and removing the maximum and minimum values. And eight samples (aging treated for from 0 to 14h at 165 °C) were tested microhardness.

 

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper "Investigation of the effect of heat treatment on the microstructures and mechanical properties of Al-Si13-Cu5.0-Ni2 alloys" describes the new aluminium alloy with enhanced mechanical properties. The authors investigated different heat treatment and determined the optimal mode. The paper is well written and may be accepted for publication. However, additional description of some points should be added accordingly following comments:

1. The authors not correctly determined the fracture strain in Figures 3a and 6a. The elastic deformation should be also considered. The line which determines the fracture strain should be not vertical but parallel to the elastic part of the deformation curve. Correct fracture strain is significantly smaller than presented by the authors.
2. It is needed to give the yield strength values. This mechanical property is more significant for constructional materials than ultimate strength.
3. The Orowan equation is not applicable for the ultimate tensile strength. It describes the contribution of the particles to yield strength.
4. The authors wrote that they used the Orowan equation for the calculation, however, calculated values of Δσ were not provided.
5. Minor corrections are also required:

• It is better to use the name of the alloy such as Al-13Si-5Cu-2Ni. The low indexes in the composition are usually used as atomic per cents.
• In Table 1 only one alloy presented, however in the title and the text of the manuscript was used term “alloys”. The authors should use the singular term.

Author Response

Response to the reviewer’s comments

Thank you for your comments. We thank the reviewer very much for the encouraging comments and recognition of our work. They are very insightful and constructive to improve our manuscript. We have carefully revised the manuscript according to the comments. The following is a point-to-point response to your comments.

Reviewer's comments:

Reviewer #2:

1. The authors not correctly determined the fracture strain in Figures 3a and 6a. The elastic deformation should be also considered. The line which determines the fracture strain should be not vertical but parallel to the elastic part of the deformation curve. Correct fracture strain is significantly smaller than presented by the authors.

 

Reply：

  Thank you very much for your professional and careful comments. It is important to consider the elastic deformation. Elongation is the percentage of plastic strain at fracture. Fracture strain includes elastic strain and plastic strain. Elongation values were added in Table 3 and Table 4. According to your professional suggestions, we have revised this problem, as follows:

 

 

 

Table 3. Data of the tensile strength and fracture strain of the Al-Si₁₃-Cu_5.0-Ni₂ alloys solution treated at different temperatures for 8 h and 165 °C aging for 10 h

Sample	Temperature (°C)	Yield Strength (MPa)	Tensile strength (MPa)	Elongation (%)	Fracture strain (%)
a	480	203+10 -14	352+11 -17	2.9+0.5 -0.3	4.8+0.4 -0.1
b	490	212+9 -12	365+7 -22	3.6+0.4 -0.1	5.3+0.2 -0.9
c	500	223+10 -16	371+7 -16	3.0+0.3 -0.2	5.5+0.3 -0.1
d	510	225+11 -7	383+14 -22	2.8+0.1 -0.4	5.7+0.7 -1.1
e	520	173+8 -7	332+4 -14	3.7+0.2 -0.5	5.6+0.2 -0.3

Table 4. Data of the tensile strength and fracture strain of Al-Si₁₃-Cu_5.0-Ni₂ alloys under different solid solution treatment time at 510 °C

Sample	Time (h)	Yield Strength (MPa)	Tensile strength (MPa)	Elongation (%)	Fracture strain (%)
a	2	186+13 -7	363+3 -16	3.7+0.7 -0.7	4.9+0.5 -0.8
b	4	205+12 -11	365+7 -8	3.5+1.2 -0.5	4.9+0.7 -0.6
c	6	218+10 -8	375+10 -12	3.5+1.1 -0.7	4.9+0.4 -1.1
d	8	237+9 -11	385+11 -27	4.5+1.4 -0.5	6.0+1.4 -0.7
e	10	225+11 -7	383+14 -22	2.8+0.1 -0.4	5.7+0.7 -1.1
f	12	199+10 -5	368+12 -18	3.3+0.3 -0.7	5.7+1.4 -1.0
g	14	191+6 -11	364+9 -17	2.5+0.7 -0.7	5.1+0.5 -0.6

See in Lines 184-189 on Page 6:

From Figure 3(b), when the solid solution treatment temperature is 510 °C, the optimum tensile properties of the alloys are obtained with maximum values of 225 MPa (yield strength), 383 MPa (tensile strength), 2.8 % (elongation) and 5.7% (fracture strain). The yield strength, tensile strength, elongation and fracture strain of the alloy solution treated at 520 °C are 193 MPa, 332 MPa, 2.7 % and 5.6%, respectively, which are lower than those at 510 °C.

See in Lines 259-261 on Page 9:

When the solid solution treatment time is 8 h, the optimum tensile properties of the alloys are obtained with maximum values of 237 MPa (yield strength), 385 MPa (tensile strength), 4.5% (elongation) and 6.0% (fracture strain).

 

2. It is needed to give the yield strength values. This mechanical property is more significant for constructional materials than ultimate strength.

Reply:

  Thank you very much for your professional and careful comments. The yield strength values are added in Table 3 and Table 4, and we have added the change yield strength in paper, as follows:

 

Table 3. Data of the tensile strength and fracture strain of the Al-Si₁₃-Cu_5.0-Ni₂ alloys solution treated at different temperatures for 8 h and 165 °C aging for 10 h

Sample	Temperature (°C)	Yield Strength (MPa)	Tensile strength (MPa)	Elongation (%)	Fracture strain (%)
a	480	203+10 -14	352+11 -17	2.9+0.5 -0.3	4.8+0.4 -0.1
b	490	212+9 -12	365+7 -22	3.6+0.4 -0.1	5.3+0.2 -0.9
c	500	223+10 -16	371+7 -16	3.0+0.3 -0.2	5.5+0.3 -0.1
d	510	225+11 -7	383+14 -22	2.8+0.1 -0.4	5.7+0.7 -1.1
e	520	173+8 -7	332+4 -14	3.7+0.2 -0.5	5.6+0.2 -0.3

 

Table 4. Data of the tensile strength and fracture strain of Al-Si₁₃-Cu_5.0-Ni₂ alloys under different solid solution treatment time at 510 °C

Sample	Time (h)	Yield Strength (MPa)	Tensile strength (MPa)	Elongation (%)	Fracture strain (%)
a	2	186+13 -7	363+3 -16	3.7+0.7 -0.7	4.9+0.5 -0.8
b	4	205+12 -11	365+7 -8	3.5+1.2 -0.5	4.9+0.7 -0.6
c	6	218+10 -8	375+10 -12	3.5+1.1 -0.7	4.9+0.4 -1.1
d	8	237+9 -11	385+11 -27	4.5+1.4 -0.5	6.0+1.4 -0.7
e	10	225+11 -7	383+14 -22	2.8+0.1 -0.4	5.7+0.7 -1.1
f	12	199+10 -5	368+12 -18	3.3+0.3 -0.7	5.7+1.4 -1.0
g	14	191+6 -11	364+9 -17	2.5+0.7 -0.7	5.1+0.5 -0.6

 

See in Lines 184-189 on Page 6:

From Figure 3(b), when the solid solution treatment temperature is 510 °C, the optimum tensile properties of the alloys are obtained with maximum values of 225 MPa (yield strength), 383 MPa (tensile strength), 2.8 % (elongation) and 5.7% (fracture strain). The yield strength, tensile strength, elongation and fracture strain of the alloy solution treated at 520 °C are 193 MPa, 332 MPa, 2.7 % and 5.6%, respectively, which are lower than those at 510 °C.

See in Lines 259-261 on Page 9:

When the solid solution treatment time is 8 h, the optimum tensile properties of the alloys are obtained with maximum values of 237 MPa (yield strength), 385 MPa (tensile strength), 4.5% (elongation) and 6.0% (fracture strain).

 

3. The Orowan equation is not applicable for the ultimate tensile strength. It describes the contribution of the particles to yield strength.

Reply:

  Thank you very much for your professional comments. The Orowan equation is used to describe the contribution of the particles to yield strength. According to your professional suggestions, we have revised this problem, as follows:

See in Lines 309-311 on page 11:

It is known that a smaller diameter and greater number density for the θ' precipitated phases can produce a more significant strengthening effect to improve the yield strength.

 

4. The authors wrote that they used the Orowan equation for the calculation, however, calculated values of Δσ were not provided.

Reply:

  Thank you very much for your professional comments. The Orowan equation is used to calculate values of Δσ. We can quantitatively estimate the contribution to the yield strength of θ΄ phases. According to the reviewer's professional suggestions, we have revised this statement, as follows:

See in Lines 311-313 on page 11:

Δσ_θ΄ is 70 MPa, 83 MPa and 75 MPa when aging time is 6 h,10 h, 14 h through Equation (1), respectively.

5. It is better to use the name of the alloy such as Al-13Si-5Cu-2Ni. The low indexes in the composition are usually used as atomic per cents.

Relpy:

  Thank you very much for your careful comments. Following your advice, we have revised the name of alloy through the full text, replacing Al-Si₁₃-Cu_5.0-Ni₂ with Al-13Si-5Cu-2Ni, and we have carefully checked all the places relating to this issue and we make sure that the problem has been solved.

 

6. In Table 1 only one alloy presented, however in the title and the text of the manuscript was used term “alloys”. The authors should use the singular term.

Relpy:

Thank you very much for your careful comments. According to your professional comments, We carefully checked the use of singular and plural term “alloys” in the paper and completed this revisions.

Author Response File: Author Response.pdf

Reviewer 3 Report

There is a sentence in the abstract, which is not readable.> “The results show that the size of eutectic silicon decreased with increasing solid solution treatment temperature until 510 °C and then increased”. Please improve that.

The authors mentioned: “The eutectic silicon size of as-cast alloy was 10.1 μm, and then the eutectic silicon was 6.5 μm under the solid solution treatment at 510 °C.” Please give also a notion of morphology of these particles either before or after solution treatment.

Please give the purities of the elements used to prepare the alloy. Which casting method was used?

Please why include Table 5 if the alloys and methods are so different to be compared to the present results.

Please replace “Temperature (°C)” with Time (hours) in table 4.

Does it make sense to perform aging if the tensile properties are the same as for solutionized samples?

Author Response

Response to the reviewer’s comments

Thank you for your comments. They are very insightful and constructive to improve our manuscript. We have carefully revised the manuscript according to the comments. The following is a point-to-point response to your comments.

Reviewer's comments:

Reviewer #3:

1. There is a sentence in the abstract, which is not readable. “The results show that the size of eutectic silicon decreased with increasing solid solution treatment temperature until 510 °C and then increased”.

Reply:

  Thank you very much for your professional and careful comments. In Figure 2(g), it showed the change of eutectic silicon size under different solid solution temperatures. The size of eutectic silicon decreased with the increase of temperature before 510 °C. When temperature was 520 °C, the size of eutectic silicon increased. The smallest average eutectic silicon size is 6.5 μm when temperature is 510 °C. We have revised this statement, as follows:

 

See in Lines 11-13 on Page 1:

The results show that the size of eutectic silicon decreased with solid solution treatment temperature increasing until 510 °C. Subsequently, the eutectic silicon size continued to increase as the temperature increased to 520 °C.

 

2. The authors mentioned: “The eutectic silicon size of as-cast alloy was 10.1 μm, and then the eutectic silicon was 6.5 μm under the solid solution treatment at 510 °C.” Please give also a notion of morphology of these particles either before or after solution treatment.

Reply:

  Thank you very much for your professional comments. It is necessary to describe the morphology of the eutectic silicon. We have added the detailed description of the eutectic silicon and the method of measure the size of the eutectic silicon, as follows:

 

See in Lines 13-15 on Page 1:

Initially, the acicular eutectic silicon of the as-cast alloy was 10.1 μm in size. After the solid solution treatment at 510 °C, the eutectic silicon size was reduced to 6.5 μm.

 

See in Lines 165-166 on Page 5:

The size of the eutectic silicon is obtained by measuring the maximum length of the acicular particles.

3. Please give the purities of the elements used to prepare the alloy. Which casting method was used?

Reply:

  Thank you very much for your careful comments. The material purities and casting method is important, which should be written in the articles, as follows:

 

See in Lines 95-98 on Page 4.

The materials used in this research were commercial pure Al ingots, Al-17Si alloys, copper scraps and nickel, and the purities of all materials used is 99.9 %. Al-13Si-5Cu-2Ni alloy were fabricated by steel mold casting.

 

4. Please why include Table 5 if the alloys and methods are so different to be compared to the present results.

Reply:

  Thank you very much for your professional comments. In Table 5, most of the alloys are eutectic Al-Si alloys, and most of them contain the element of Cu. Compared to other methods (for example, inoculation and extrusion), T6 heat treatment is a simple and effective method to significantly improve the mechanical properties of alloys. Although the work were compared to different alloys and methods. In order to make the alloy composition more similar, we have modified the alloy used to compare and reanalyzed the data. The Figure 7 and Table 5 have been revised, as follow:

 

Figure 7. The mechanical properties and hardness of Al-13Si-5Cu-2Ni alloy solid solution treated at 510 °C for 8 h and 165 °C aging for different hours: (a) the engineering stress-strain curves; (b) bar graph of tensile strength and fracture strain; (c) hardness of aging different hours; (d) contrast diagram of different strengthening methods for Al alloys with this work

 

Table 5 Comparison of different strengthening methods with this work for Al alloys

Alloys	Reinforcement	UTS (MPa)	FS (%)	Ref.
Our work		385	6.0
Al–11.3Si–1.79Cu–0.79Zn–0.04Sr	alloys of Sr	157.8	1.29	[40]
Al-13Si-4Cu-2Ni-0. 8Mg-0.02Sr	alloys of Sr	249	0.97	[41]
Al–10.56Si–1.91Cu–0.21Mg–0.28Mn	extruded	233	6.4	[42]
Al–13.86Si–0.14Fe–0.005Cu	Strain induced melt activation	189.79	9.72	[43]
Al–13.86Si–0.14Fe–0.005Cu		139.29	4.18	[43]
Al-18Si	1.0wt.%SiCp	172	6.8	[44]
Al-Si11.5-Cu1.1-Mg1.2-Ni1.5	T5	318	5.6	[45]

 

5. Please replace “Temperature (°C)” with Time (hours) in table 4.

Reply:

  Thank you very much for your valuable comments. According to your careful advice, Table 4 has been modified, as follows:

 

See in Lines 268 on Page 9

Table 4. Data of the tensile strength and fracture strain of Al-13Si-5Cu-2Ni alloy under different solid solution treatment time at 510 °C

Sample	Time (h)	Yield Strength (MPa)	Tensile strength (MPa)	Elongation (%)	Fracture strain (%)
a	2	186+13 -7	363+3 -16	3.7+0.7 -0.7	4.9+0.5 -0.8
b	4	205+12 -11	365+7 -8	3.5+1.2 -0.5	4.9+0.7 -0.6
c	6	218+10 -8	375+10 -12	3.5+1.1 -0.7	4.9+0.4 -1.1
d	8	237+9 -11	385+11 -27	4.5+1.4 -0.5	6.0+1.4 -0.7
e	10	225+11 -7	383+14 -22	2.8+0.1 -0.4	5.7+0.7 -1.1
f	12	199+10 -5	368+12 -18	3.3+0.3 -0.7	5.7+1.4 -1.0
g	14	191+6 -11	364+9 -17	2.5+0.7 -0.7	5.1+0.5 -0.6

 

6. Does it make sense to perform aging if the tensile properties are the same as for solutionized samples?

Reply:

  Thank you very much for your professional comments. In this work, my all samples were tested after T6 heat treatment. We optimized the temperature of solution treatment under a certain aging treatment, and then optimized the aging time on the basis of the previously optimal solution treatment. In section 3.2, the samples were tested under aging treatment at 165 °C for 10h, and then optimized the solution treatment temperature. In section 3.3, we used the optimal solution treatment(solution treated at 510 °C for 8 h) previously obtained to optimize the aging time. The solid solution treatment promotes the solid solution of the elements into the matrix. Fine and dispersed strengthened phase could be precipitated during aging treatment, which significantly increase the strength of the alloys.

See in Lines 177-179 on Page 6:

Figure 3 shows the mechanical properties of the Al-13Si-5Cu-2Ni alloy solution treated at different temperatures for 8 h and 165 °C aging for 10 h.

See in Lines 207-208 on Page 7:

Figure 4 shows the microstructures of the Al-13Si-5Cu-2Ni alloy solid solution treated at 510 °C for 8 h and aging treated at 165 °C for different hours.

See in Lines 252-253 on Page 9:

Figure 7. The mechanical properties and hardness of Al-13Si-5Cu-2Ni alloy solid solution treated at 510 °C for 8 h and 165 °C aging for different hours: (a) the engineering stress-strain curves; (b) bar graph of tensile strength and fracture strain; (c) hardness of aging different hours; (d) contrast diagram of different strengthening methods for Al alloys with this work

 

Reviewer 4 Report

In this work, the authors studied the effect of heat treatment conditions on the microstructure and mechanical properties of Al-Si-Cu-Ni Alloys. Optimum condition was found yielding a tensile strength and strain of 385 MPa and 6%, respectively. The experiments were conducted in a good standard, however, the quality in manuscript writing should be improved. 

Here are my comments,

1. The language of this manuscript should be improved. It is recommended to re-write the abstract in a clearer manner. For example, "The results show that the size...solid solution treatment at 510C". These two sentences should be combined into one. Also, give a bit more context before mentioning "theta phase" so readers could understand why it is worth studying. 
2. Introduction part could be shortened to highlight the motivation of this work, e.g. why it is worth conducting this work. 
3. Figure 1. (d) (e) it is compositional analysis by EDS, not phas analysis
4. Table 2. caption. The authors should check everything before submission. It is unacceptable to submit it with this mistake: "This is a table. Tables should be placed in the main text near to the first time they are cited."
5. Figure 2. add error bar to the graph (g).
6. Format issue: leave sufficient gaps around figures. See Figure 4 for example. table 5. 
7. Discussion section should be separated from results. 

Author Response

Response to the reviewer’s comments

Thank you for your comments. They are very insightful and constructive to improve our manuscript. We have carefully revised the manuscript according to the comments. The following is a point-to-point response to your comments.

Reviewer's comments:

Reviewer #4:

1. The language of this manuscript should be improved. It is recommended to re-write the abstract in a clearer manner. For example, "The results show that the size...solid solution treatment at 510C". These two sentences should be combined into one. Also, give a bit more context before mentioning "theta phase" so readers could understand why it is worth studying.

Reply:

Thank you very much for your careful comments. According to your careful advice, the language of this manuscript have improved. We have uploaded the editing certificate. And add the context about the effect of theta phase, as follows:

See in Lines15-17 on Page 1:

The θ΄ phase is the main strengthening phase in the alloy, therefore, the effect of aging treat-ment on θ΄ phases was explored. As the aging time increased, the diameter, length and fraction volume of the θ΄ phases was found to increase.

 

 

 

editing certificate, as follows:

 

2. Introduction part could be shortened to highlight the motivation of this work, e.g. why it is worth conducting this work.

Reply:

Thank you very much for your careful comments. According to your careful comments, this problems has been revised, as follows:

See in Lines 85-92 on Pages 2-3:

At present, many studies have been performed on the heat treatment process of Al-Si-based alloys. Al-13Si-5Cu-2Ni alloy are high copper and high nickel alloys that are applied extensively for production and have high strength at elevated temperatures. It is meaningful to explore the influence of the T6 heat treatment process on the microstructure and mechanical properties of Al-13Si-5Cu-2Ni alloy. This work also provides a theoretical basis for the heat treatment process of Al-Si-Cu alloys. In the present work, the heat treatment process for Al-13Si-5Cu-2Ni alloy is studied to optimize the heat treatment process, which can provide theoretical and data support for the application of these alloys.

 

3. Figure 1. (d) (e) it is compositional analysis by EDS, not phase analysis.

Reply:

Thank you very much for your professional and careful comments. According to the reviewer's professional suggestions, we have revised this Figure 1, as follows:

 

Figure 1. Microstructure and phase analysis of as cast Al-13Si-5Cu-2Ni alloys: (a) low magnification microstructure, (b) local magnification in figure (a), (c) XRD pattern,(d) C compositional analysis by EDS and (e) D compositional analysis by EDS.

See in Lines 126-127 on Page 3:

The microstructure of as-cast Al-13Si-5Cu-2Ni alloy and phase compositional analysis are shown in Figure 1.

4. Figure 2. add error bar to the graph (g).

Reply:

Thank you very much for your professional and careful comments. According to the reviewer's professional suggestions, we have added error bar and then revised this Figure 3(g), as follows:

 

Figure 3. Microstructures of Al-Si₁₃-Cu_5.0-Ni₂ alloys solid solution treated at different temperatures for 8 h and 165 °C aging for 10 h and the size of eutectic silicon of alloys: (a) as cast; (b) 480 °C; (c) 490 °C; (d) 500 °C; (e) 510 °C; (f) 520 °C; (g) the size of eutectic silicon.

 

5. Format issue: leave sufficient gaps around figures. See Figure 4 for example. table 5.

Reply:

Thank you very much for your comments. According to your exhaustive suggestions, we have revised this format issue.

 

6. Discussion section should be separated from results.

Reply:

Thank you very much for your profession comments. According to your careful advice, we thought carefully about this statement. In this paper, the part of strengthening mechanism is more suitable as the section of discussion. And we have modified this part, as follows:

See in Lines 291-314 on Pages 11:

The solid solution treatment promotes the solid solution of the elements into the matrix and provides the driving force for the fine and dispersed second phase precipitations during aging treatment. As shown in Figure 8, there exist Al₂Cu phases and Al₇Cu₄Ni phases at the grain boundaries of the as-cast Al-Si₁₃-Cu_0.5-Ni₂ alloys. In addition, the solid solution treatment also leads to passivation of primary silicon and fragmentation and spheroidization of eutectic silicon. This reduces the split between silicon phases and the matrix in the Al-Si alloys. Therefore, the size of eutectic silicon is the smallest when solid solution treatment temperature is 510 °C, and then the tensile strength of sample solution treated at 510 °C is the highest. The θ΄ phases precipitated during aging treatment pin the dislocations under load and then improve the strength of the alloys which is called Orowan strengthening. We used the modified Orowan equation to calculate the Orowan stress due to plate-like θ΄ precipitate strengthening (Δσ_θ΄) according to the following modified Orowan equation[39, 46-48]:

                                   (1)

where M is the Taylor factor for Al (approximately equal to 3[39]), G is the shear modulus (26 GPa), ν is the Poisson’s ratio (1/3 for Al[39]), b is the Burgers vector (0.286 nm for Al[39]), a is the aspect ratio of the precipitates (a= d/t, d and t are the diameter and thickness of the precipitates, respectively) and f is the volume fraction of the θ΄ precipitates. It is known that a smaller diameter and greater number density for the θ' precipitated phases can produce a more significant strengthening effect to improve the yield strength. Δσ_θ΄ is 83 MPa when aging time is 10 h through Equation (1). With increasing aging treatment time, the diameter of the θ΄ phase increases. A suitable aging treatment is extremely important.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors significantly improved the manuscript. The paper may be accepted in the current state.

Reviewer 4 Report

The authors have made substantial efforts in revising the manuscript to a satisfactory extent. Just one more comment on the English writing, which the reviewer strongly believes, still needs improvement. 

- An English "certificate", which is also outdated, does not necessarily certify anything. Probably only the basic language, e.g., spelling, grammar, etc. was checked by this "highly qualified native English speaking person" who might know nothing about metals or alloys.