Research Status and Prospective Properties of the Al-Zn-Mg-Cu Series Aluminum Alloys

Round 1

Reviewer 1 Report

The manuscript is devoted to the analysis of the influence of alloying elements on the physical and mechanical properties of Al alloys of the 7xxx series.

There are several comments.

1. The purpose of this review on alloying aluminum alloys of the 7xxx series is not entirely clear.

2. Alloys of the Al-Zn-Mg-Cu system are superplastic. It would be interesting to analyze the effect of alloying elements on the grain/subgrain size and on the temperature at which SP properties appear.

3. In the section on the effect of zinc on mechanical properties, information on the thermal stability temperature should also be added. Zinc is the main alloying element in high-strength 7xxx alloys, the section on the effect of zinc on properties should be the main one.

Minor editing of English language required

Author Response

Reply to Academic Editor

Academic Editor Notes

The authors replied to Reviewers comments.

I have some comments for authors before publishing:

-The purpose of this review on alloying aluminum alloys of the 7xxx series is not entirely clear.

Response:  Thanks for the reviewer's kind suggestion. with the increasing of alloying element types, the phase composition and precipitation behavior in the alloy become more complex, the component differences in local areas are significant, the corrosion cracking sensitivity increases, and the contradiction between strength and corrosion performance becomes more acute. Therefore, the influence mechanism of different elements on the properties of the alloy was discussed and the range of action and the best content of elements were found to solve the contradiction between the strength, toughness and corrosion resistance of the aluminum alloy. It was an urgent problem to be solved in the development process of ultra-high strength aluminum alloy. The above content has been added to the introduction.

 

-Alloys of the Al-Zn-Mg-Cu system are superplastic. It would be interesting to analyze the effect of alloying elements on the grain/subgrain size and on the temperature at which SP properties appear.

Response:  Thanks for the reviewer's kind suggestion. After the strain value w-as 1.10 (corresponding to 200% elongation), the transmission electron microgr-aph that was obtained from the measurement part of the Al-Zn-Mg-Cu-0.10sc-0.10Zr alloy sample could be observed that a large number of fine Al₃Sc_xZr_1-x p-articles with Ashby-Brown contrast were evenly distributed inside the particles (black circle) and remained almost constant in size (10-20nm) during deformat-ion. From HRTEM image of Al₃Sc_xZr_1-x particle, the Al₃Sc_xZr_1-x particles were spherical with a size of about 15 nm and were completely coherent with the aluminum matrix alloy. These coherent particles strongly fixed dislocations and grain boundaries, which resulted in the controlled growth of microscale grains. Therefore, adding an appropriate amount of Sc to the aluminum alloy could s-ignificantly improve the plastic properties of the alloy. Pictures and text about t-his content have been added to the text.

-In the section on the effect of zinc on mechanical properties, information on the thermal stability temperature should also be added. Zinc is the main alloying element in high-strength 7xxx alloys, the section on the effect of zinc on properties should be the main one.

Response:  Thanks for the reviewer's kind suggestion. Al-Mg-Cu alloy with a-dded Zn still maintained good properties after aging at 125℃ for 192 h. A la-rge number of small cubic precipitates were uniformly distributed in the alumi-num matrix. And its structure was stable, which could greatly prevent the def-ormation at high temperature. The thermal stability of the alloy was significan-tly improved Pictures and text about t-his content have been added to the text.

 

Reviewer 2 Report

In my opinion, the review lacks graphic materials on the structure of the alloys, which significantly affects the characteristics of the alloy. The authors have references to this in the text, but I did not have a complete picture.

Author Response

Reply to Academic Editor

Academic Editor Notes

The authors replied to Reviewers comments.

I have some comments for authors before publishing:

-In my opinion, the review lacks graphic materials on the structure of the alloys, which significantly affects the characteristics of the alloy. The authors have references to this in the text, but I did not have a complete picture.

Response:  Thanks for the reviewer's kind suggestion. More than 10 images were added to show the influence of alloy elements on the change of alloy structure. At the same time, some new characteristics of alloy elements were added to make the article more rich.

Reviewer 3 Report

1.      Since the manuscript is a review article, the authors should refer to more number of previous articles in Section 2, in each addition of alloying element.

2.      Each section can be characterized into different sub-section based on their properties.

3.      The sub-section can be briefly summarized about the properties achieved with the alloying elements.

4.      Similarly, the micro-alloying element have their significant effects in achieved required goals. Those properties can be sub-categorized and should be discussed properly. While doing so, cite the important graphs, or any visual representations.

5.      The manuscript should include more images that represent the microstructural changes that occurred with the alloying elements.

6.      Overall, the manuscript contains a good amount of technical content.

 

 

Author Response

Reply to Academic Editor

Academic Editor Notes

The authors replied to Reviewers comments.

I have some comments for authors before publishing:

-Since the manuscript is a review article, the authors should refer to more number of previous articles in Section 2, in each addition of alloying element.

Response:  Thanks for the reviewer's kind suggestion. On the basis of the original literature, another 7 literatures were added, as follows:

1. Hsiao T J, Chiu P H, Tai C L, et al. Effect of Cu Additions on the Evolution of Eta-prime Precipitates in Aged AA 7075 Al–Zn–Mg–Cu Alloys. Metals. 2022, 12(12), 2120. https://doi.org/10.3390/met12122120
2. Jiao H, Chen K, Chen S, Yang Z, Xie P, Chen S. Effect of Cu on the Fracture and Exfoliation Corrosion Behavior of Al-Zn-Mg-xCu Alloy. Metals. 2018, 8(12), 1048. https://doi.org/10.3390/met8121048
3. Mondal C, Mukhopadyay A K. On the Nature of T(Al2Mg3Zn3) and S(Al2CuMg) Phases Present in As-Cast and Annealed 7055 Aluminum Alloy. Materials Science and Engineering: A, 2005, 391,367-376. https://doi.org/10.1016/j.msea.2004.09.013
4. Duan Y L, Fu G, Zhou L Q, et al.Achieving high superplasticity of a traditional thermal–mechanical processed non-superplastic Al–Zn–Mg alloy sheet by low Sc additions.Journal of Alloys & Compounds, 2015, 638, 364-373. https://doi.org/10.1016/j.jallcom.2015.03.090
5. Kim K H .Effects of Sc and Be Microalloying Elements on Mechanical Properties of Al-Zn-Mg-Cu (Al7xxx) Alloy.Metals, 2023, 13. https://doi.org/10.3390/met13020340
6. Won S J, So H, Han J W, Oh S J, et al. Roles of Sc and Ag Microalloying Elements in the Mechanical Properties of Al-Zn-Mg-Cu (Al7xxx) Alloy. Metals, 2023, 13(2), 244. https://doi.org/10.3390/met13020244
7. Mao J W, Wen S P, Liang S S, et al. Effect of Zn content and Sc、Zr addition on microstructure and mechanical properties of Al-Zn-Mg-Cu alloys. Journal of Alloys & Compounds, 2023, 946, 169401. https://doi.org/10.1016/j.jallcom.2023.169401

 

-Each section can be characterized into different sub-section based on their properties.

Response:  Thanks for the reviewer's kind suggestion. In the original text, the parts of each element were divided into several small parts according to the problems explored.

 

-The sub-section can be briefly summarized about the properties achieved with the alloying elements.

Response:  Thanks for the reviewer's kind suggestion. At the end of the main alloy elements, microalloy elements and rare earth elements, the summary was added, as follows:

1. Cu played an important role in the corrosion performance of the alloy, which could adjust the trend of Zn and Mg to decrease the corrosion resistance when the strength and hardness were increased. At the same time, Zn could make the alloy have high plasticity properties, which was expected to achieve a balance between ductility and strength. Therefore, adjusting the proportion between the main elements and finding the threshold between the proportion of elements could effectively solve the contradiction between strength and toughness and corrosion resistance.
2. The impurity elements Fe and Si that were controlled in a certain range could not only reduce the appearance of alloy cracks, but also improve the fatigue life and strength of the alloy. Ag played an important role in improving resistance to stress corrosion and solution corrosion. At the same time, the ductility decrease was small. Ti and Ni played a crucial role in improving strength and reducing thermal cracking sensitivity. However, the role of Ag, Ti and Ni also had a threshold and the right amount of addition could play its most effective role. And balance the relationship between mechanical properties.
3. Sc played an important role in refining grain, improving toughness and corrosion resistance. However, due to its high cost, it was not conducive to widespread industrial application and it was necessary to achieve the same effect by low-cost rare earth elements or composite addition. For example, the combined addition of Sc and Zr could not only promote precipitation strengthening, but also improve thermal stability. Other rare earth elements Sm, Er, La, Ce, Y and Ta all played different roles in refining grains.Among them, Er and Ce could greatly improve the corrosion resistance of the alloy. Sm and La played a role in improving the tensile strength.It is important to clarify the main functions and effects of each rare earth element. Compound addition of rare earth elements that reduced cost and balanced performance were urgent problems in the development of alloys

 

-Similarly, the micro-alloying element have their significant effects in achieved required goals. Those properties can be sub-categorized and should be discussed properly. While doing so, cite the important graphs, or any visual representations.

Response:  Thanks for the reviewer's kind suggestion. The part of each microalloy element was divided into several small parts to explore the balance between strong toughness and corrosion resistance and the characteristics of each element were discussed. A large number of microstructure maps were added to show the influence of microalloy elements on alloys.

 

-The manuscript should include more images that represent the microstructural changes that occurred with the alloying elements.

Response:  Thanks for the reviewer's kind suggestion. More than 10 images were added to show the influence of alloy elements on the change of alloy structure.

 

- Overall, the manuscript contains a good amount of technical content.

Response:  Thanks for the reviewer's kind suggestion.

 

Reviewer 4 Report

The paper presents an interesting topic but it is not up to standard. Severe problems with the quality of English appear right in the abstract - for example the use of words like "huge" and "so on" that are not up to standard in science publications. The introduction presents statements without any reference. Several of the images presented have poor quality.

As stated previously.

Author Response

Reply to Academic Editor

Academic Editor Notes

The authors replied to Reviewers comments.

I have some comments for authors before publishing:

-The paper presents an interesting topic but it is not up to standard. Severe problems with the quality of English appear right in the abstract - for example the use of words like "huge" and "so on" that are not up to standard in science publications. The introduction presents statements without any reference. Several of the images presented have poor quality.

Response:  Thanks for the reviewer's kind suggestion. English wording was reworked and some grammatical errors were also made over. The introduction was improved, as follows：The main elements of Al-Zn-Mg-Cu alloy include Al, Zn, Mg and Cu, which contain trace amounts of Si and Fe (usually present as impurity elements). The types and contents of trace elements are different among different brands, which leads to the different mechanical properties of the alloy. Therefore, the mechanical properties of the alloy could be improved by adjusting the composition of Al-Zn-Mg-Cu alloy, selectively introducing trace alloying elements, reducing the impurity content and realizing the reasonable distribution of precipitated phase. Rare earth elements played a more significant role in this process due to their special electronic structure and chemical properties. However, with the increasing of alloying element types, the phase composition and precipitation behavior in the alloy became more complex. The component differences in local areas were significant. The corrosion cracking sensitivity increased and the contradiction between strength and corrosion performance became more acute. Therefore, the influence mechanism of different elements on the properties of the alloy was discussed and the range of action and the best content of elements were found to solve the contradiction between the strength, toughness and corrosion resistance of the aluminum alloy. It was an urgent problem to be solved in the development process of ultra-high strength aluminum alloy.

  The pictures of the original text were modified and a large number of pictures about the alloy microstructure were added to directly show the role of the alloy elements.

Round 2

Reviewer 1 Report

 Accept in present form

Author Response

Thanks for the reviewer's comments.

Reviewer 4 Report

Paper accepted following improvements and considering other reviewers opinion.

Author Response

Thanks for the reviewer's comments.