Study on the Correlation between the Microstructure Characteristics and Corrosion Behaviors of 2A12-T4 Aluminum Alloy under Thermal Strain
Round 1
Reviewer 1 Report
It is a paper about the correlation between microstructure characteristics and corrosion behavior of 2A12 aluminum alloy under thermal strain.
In the paper, the authors used the welding thermal simulation technique to prepare enlarged TMAZ specimens with different peak temperatures and tensile strain. Subsequently, the authors investigated the relationship among thermo-mechanical parameters evolution of microstructure characteristics-corrosion behavior. Thus, they achieved results and conducted conclusions providing the optimization of friction stir welding parameters.
The introduction provides sufficient background and includes relevant references. The paper's subject area and presentation quality allow the article can be quite interesting for inner circle potential readers.
In the manuscript, all necessary information is captured by 7 figures and 3 tables. There are 25 references; all of them are reflected in the text.
In the reviewer's opinion, the manuscript that pretends to be a science article should include more scientific conceptualization in the Materials and Methods section adequately described. The Conclusion section should have a more detailed summary. Moreover, Table 1 has some typos, and the caption should be capitalized in the first letter.
Author Response
Response to Reviewer Comments
(All revisions in this manuscript are shown in blue font.)
Point 1: The manuscript that pretends to be a science article should include more scientific conceptualization in the Materials and Methods section adequately described.
Response 1: We thanks for reviewer’s suggestion for improvement of the manuscript. We have added more detailed information about materials and methods.
Point 2: The conclusion section should have a more detailed summary.
Response 2: We thank the reviewer for this valuable comment. We have refined the conclusion.
Point 3: Table 1 has some typos, and the caption should be capitalized in the first letter.
Response 3: Thanks for the suggestion. We have corrected these errors.
Reviewer 2 Report
The paper describes experiments meant to simulate the TMAZ corrosion behavior in AA 2A12. The approach is described clearly, but I have a concern about the premise behind the experimental design. The authors have assumed that straining the specimens in uniaxial tension would be a good simulation of the strain in the TMAZ in a friction stir weld. However, the deformation modes are quite different in these two cases. Friction stir welding imparts a shear strain on the material, including in the TMAZ. The authors have not made the case that uniaxial tension is an appropriate simulation for the shear created by FSW. While the work that was done is of good quality, and the conclusions apply to the experimental results produced, the authors need further support from the literature, or their own analysis, to support the use of uniaxial tension in their experimental simulations. Otherwise, the premise that their results can be applied to friction stir welded AA 2A12 is not supported.
Author Response
Response to Reviewer Comment
(All revisions in this manuscript are shown in blue font.)
Point 1: The authors have assumed that straining the specimens in uniaxial tension would be a good simulation of the strain in the TMAZ in a friction stir weld. Friction stir welding imparts a shear strain on the material, including in the TMAZ. The authors have not made the case that uniaxial tension is an appropriate simulation for the shear created by FSW. The premise that their results can be applied to friction stir welded AA 2A12 is not supported.
Response 1: Thanks for this suggestion. I think you may have misunderstood me. I did not simulate TMAZ by thermal simulation technology, but by simulating the thermodynamic coupling state of TMAZ under both heat and stress, so as to study the correlation between microstructure evolution and corrosion behavior under thermal strain. The reason why I mentioned HAZ and the corrosion resistance of TMAZ and HAZ is very different from that of the base metal, and when a material is subjected to both heat and stress, the grain morphology, structure type and stress-strain state of the material will change, which are the reasons for the change of its corrosion resistance. Therefore, I got inspiration from the stress condition of TMAZ to study the correlation between thermodynamic coupling on microstructure evolution and corrosion behavior of aluminum alloy. If the corrosion behavior of TMAZ is specifically studied, the TMAZ can be cut off for micro-corrosion experiments.
Reviewer 3 Report
The article describes valuable experiment of thermal strain treated samples. Authors try to correlate to correlate the microstructure and corrosion behaviour. In my opinion this topic deserves to slight improvements on research methods to prove the authors colciusions. Below I list my major comments:
1. The article requires some writing corrections. Even in the first sentence there are we have repetition "manufacturing industry", and in the second "aluminium alloy". The article should be proofreaded with care.
2. Instead of citing 13 papers in 3 sentences, I suggest to refer to rewiev and perspectives papers or precisely discuss the value of cited papers.
3. The SEM and TEM methods of sample preparation and observations was not really described.
4. Chapter 3.1.1 discuss "larger" or "coarsened" grains. I suggest to measure and compare grain size numerically, not based on subjective observation.
5. Chapter 3.1.2 show "second phase" morphologies, but we can see almost nothing, because magnification of fig. 2 is closer to light microscopy than SEM possibilities. Talking about three morphologies based on one 2D cross-section is not really proper - authors observe not the precilitate but only its section, which not really tell us the shape of the crystal. What was sample cross-section orientation?
6. Then - authors discuss "second phase" but mention "the components of the second phase are mainly θ(Al2Cu) and S(Al2CuMg)", so we have more than second phase. Maybe the phrase like "precipitates" is more clear than "second phase" ?
7. Authors discuss disslocation densities based on TEM images. How the authors controll the sample thickness in place of observation? For compare different dislocation structures we need to be sure that the thickness is the same, because we observe 2D representation of sample volume.
8. Why authors did not recognize precipitate phases via SAED?
9. If you discuss change of the shape/size on TEM, please measure it and compare values with some statistics.
10. Chapter 3.2.2. Discussing the corrosion mechanism on sample surface could easily lead to wrong conclusions. At the same time, the cross-sections from the same samples could give us information about the corrosion mechanism and the depth.
11. Are figs 6-7 produced via SE or BSE electrons? It is not specified in methods chapter
Author Response
Response to Reviewer 3 Comments
(All revisions in this manuscript are shown in blue font.)
Point 1: The article requires some writing corrections. Even in the first sentence there are we have repetition "manufacturing industry", and in the second "aluminium alloy". The article should be proofreaded with care.
Response 1: We thanks for reviewer’s suggestion for improvement of the manuscript. We have carefully proofread and revised the statement.
Point 2: Instead of citing 13 papers in 3 sentences, I suggest to refer to review and perspectives papers or precisely discuss the value of cited papers.
Response 2: Thanks for this suggestion. We have removed unnecessary citations to the paper.
Point 3: The SEM and TEM methods of sample preparation and observations was not really described.
Response 3: Thanks for this suggestion. I am sorry that I did not specify in detail the procedure of TEM experiment, including how to control the thickness of observed samples, but I have made a detailed supplement to it (the supplement is as follows: Transmission electron microscope (TEM) was used to observe the size of the dislocation structure and dislocation densities. In order to ensure the experiment, the thickness of the obtained thermal simulation sample was ground to 100µm, then the small wafer of Ø3mm was taken out, and the sample was analyzed by transmission electron microscopy using point solution and double spray. The electrolyte was HNO3: CH3OH= 3:7, and the acceleration voltage was 200kV under Talos F200X field emission transmission electron microscope.)
Point 4: Chapter 3.1.1 discuss "larger" or "coarsened" grains. I suggest to measure and compare grain size numerically, not based on subjective observation.
Response 4: Thanks for this suggestion. We have measured the grain size according to the line intercept method of standard GB/T 6394-2017, and compared the grain size under various parameters.
Point 5: Chapter 3.1.2 show "second phase" morphologies, but we can see almost nothing, because magnification of fig. 2 is closer to light microscopy than SEM possibilities. Talking about three morphologies based on one 2D cross-section is not really proper - authors observe not the precipitate but only its section, which not really tell us the shape of the crystal. What was sample cross-section orientation?
Response 5: Thanks for this suggestion. You are right. As for the description of the precipitated phase, I only described the morphology of the cross section of the precipitated phase. I made a mistake in my expression, and I have modified it.
Point 6: Then - authors discuss "second phase" but mention "the components of the second phase are mainly θ(Al2Cu) and S(Al2CuMg)", so we have more than second phase. Maybe the phrase like "precipitates" is more clear than "second phase" ?
Response 6: Thanks for this suggestion. My expression is wrong. I have changed the "second phase" to "precipitated phase".
Point 7: Authors discuss dislocation densities based on TEM images. How the authors control the sample thickness in place of observation? For compare different dislocation structures we need to be sure that the thickness is the same, because we observe 2D representation of sample volume.
Response 7: We thanks for reviewer’s suggestion for improvement of the manuscript.
I am sorry that I did not specify in detail the procedure of TEM experiment, including how to control the thickness of observed samples, but I have made a detailed supplement to it. For the dislocation structure, I described it based on the microstructure morphology of the cross section of the sample.
Point 8: Why authors did not recognize precipitate phases via SAED?
Response 8: Thanks for this suggestion. Because I think 2A12 aluminum alloy has been studied many times by predecessors, and the precipitate phase in it is not special, so I'm sorry for not doing SAED.
Point 9: If you discuss change of the shape/size on TEM, please measure it and compare values with some statistics.
Response 9: Thanks for this suggestion. I have measured and accurately described the precipitated phases dimension in the TEM.
Point 10: Chapter 3.2.2. Discussing the corrosion mechanism on sample surface could easily lead to wrong conclusions. At the same time, the cross-sections from the same samples could give us information about the corrosion mechanism and the depth.
Response 10: Thanks for this suggestion. I have done the corrosion depth of cross section after electrochemical test, and the effect is not obvious. Partial experimental results are shown in Figure 1. Due to the short electrochemical test time, low degree of strong polarization, scanning potential did not reach the breakdown potential, resulting in the corrosion depth is not obvious. Thank you very much for your idea. I will further study it through corrosion immersion or salt fog corrosion experiment in the following experiments.
Fig.1 corrosion morphology of cross section after electrochemical test
Point 11: Are figs 6-7 produced via SE or BSE electrons? It is not specified in methods chapter.
Response 11: Thanks for this suggestion. I have made a supplement to the methods (the supplement is as follows: After the electrochemical test, the corrosion morphology of the samples was observed by using Phenom-XL(SEM) BSD(Back-scattered) mode).
Round 2
Reviewer 3 Report
Thank you for responding to my comments. I regret that the system does not allow me to download Supplementary Material, but I trust that it was prepared with care.
