Long-Term Atmospheric Aging and Corrosion of Epoxy Primer-Coated Aluminum Alloy in Coastal Environments

Round 1

Reviewer 1 Report

The manuscript submitted to Coatings Journal is very interesting and is within the scope. Brings together important data, mainly long-term data which is, nowadays, scarce among publications focused on this subject.

The manuscript deserves publication, however before that some major concerns must be addressed correctly, namely:

1. The introduction does not reflect the actual state-of-the-art. Therefore, it should be revised and improved.
2. Please introduce a paragraph in the end of the introduction with main results and conclusions.
3. Experimental section - please introduce the number of samples tested in each analysis. Were duplicates, triplicates? This should be clearly indicated.
4. Please provide the Nyquist plots in section 3.4. Moreover, the goodness of the fitting and the errors regarding the elements of the EEC must be introduced in a table.
5. Regarding the sectional characterization can the authors provide the changes in the thickness coating through the years?
6. Regarding the AFM data please introduce a table with the roughness parameters (Ra and Rmax as well as the error of the obtained data)
7. The conclusions need to be shortened. Part of this should be moved to the data discussion.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

The current paper investigates the effects of exposing epoxy primer coated Al alloy in coastal conditions for certain periods of time. The aim is to determine the long-term exposure of this coated alloy for such atmospheric conditions that usually make metals susceptible to corrosion and electrochemical impedance.  The study found that the angle of exposure can have important effects while the fractal dimensions increased with increased duration of exposure. The coating was also affected by the exposure duration due to synergistic effects such as ageing and post curing phenomena.

The abstract is written to good standard but can be more detailed in terms of what was specifically concluded from the exposure and analysis results in terms of corrosion and electrochemical analysis.

The authors talk about coastal conditions, to my understanding this means something near a sea environment? However, the start of the abstract is talking about exposing metals during flight in an aircraft. This kind of deviate from the main subject of the paper. Please address this issue. In the abstract say aircraft subjected to weather conditions in coastal areas or something similar.

Line 45 please avoid bulk citation unless all the references are given enough credit afterwards in the text.

In all references please leave a gap before the word and the references for example line 45 “factors[…] should be factors […].

Figure 1 can the authors explain why this certain thicknesses were applied, is it based on industrial standards or something else?

Table 1 needs a reference

Figure 2 is interesting but not necessary, it is suggested to remove it but its up to the authors to do this or not.

 Table 2 how often did the weather conditions were measured during that year?

Sine there are some formulas it is advised to add a nomenclature table at the start or end of he paper explaining all symbols and their meaning.

Line 161 are these impurities stuck to the surface or can be removed if wiped out for example?

Figure 8 is interesting but is not very clear, please enlarge the images to make it more clear.

The microcrack in figure 8 are they formed naturally under no loading or due to some loading during the test period.

Figure 9 it is not possible see anything from the micrographs in the diagram please use something more clear to better see what we are looking at here.

Check line 409 it might need rephrasing

Line 414, do you have any references to support this claim “the intensified post-curing…” or did you observe this in this study only and not in past work by other researchers or Al alloy or other types of metals?

Line 510-511 regarding these observations, do you have any similar or contradicting results from the literature that supports or disagrees with them, the discussion is well explained but there is limited effort to compare the current results with any past studies on similar work on metals and coatings in coastal environments. This issue must be addressed everywhere in the discussion section.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Manuscript reference number: coatings – 1097761, Tianyu Zhang, Teng Zhang, Yuting He, Sheng Zhang, Binlin Ma, Zhigang Gao, Long Term Atmospheric Aging and Corrosion of Epoxy Primer Coated Aluminum Alloy in Coastal Environments

General information:

The article has a scientific character. The Authors applied correct research methods and used the appropriate measuring equipment. The content of the work is logically written. The purpose of the work is not correctly formulated. The aim of the work has been achieved. The manuscript contains twenty two figures and three tables. Figures and tables are properly prepared. Authors cited fifty for literature sources. The cited literature is scientifically up-to-date and concerns the subject of the publication. Some publications are out of date. The summary of the research results has been written very lengthily, which makes it difficult to understand the relevant research results.

The article cannot be published in its current form because:

The most important part of the article should concern corrosion tests of aluminum samples after a sufficiently long exposure time in natural conditions. Unfortunately, this part of the article is unprofessionally edited and must be completed, and properly discussed.

1. The aim of the research is formulated very extensively and therefore it is difficult to find out what the most important goal of the research was.

1. The article shows that the tested materials undergo passivation under the conditions of the experiment. In this case, a very important problem of scientific importance is the depassivation process of Al alloy. Therefore, the Authors must discuss the issue of depassivation of the studied materials in depth and substantively.

1. The results of the research obtained by the Authors using the EIS method must be supplemented by quoting Nyquist plots. Then the Authors should describe and discuss the cited curves.

1. The parameters of the equivalent circuits (Fig. 15) should be determined (read), summarized in the appropriate table, and properly discussed in depth.

1. In order to increase the scientific value of the article the Authors have to calculate the values of the corrosion rate as CR (mm/year) of the tested materials, and compare them with each other and draw appropriate conclusions. In this case, the corrosion rate of the tested materials should be determined on the basis of the measurement results obtained by the electrochemical method i.e. on the basis of the potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS).

1. The kinetic parameters of the corrosion process of the tested materials should be summarized in a separate table, and thoroughly discussed.

1. The conclusions resulting from the research investigations must be supplemented, among others, the kinetic parameters of the Al alloy corrosion process under the experimental conditions should be taken into account.

Additional remarks:

1. Authors should note that articles must be cited in a specific order, for example: Liu et al. [21] (line 50) and elsewhere.
2. Some of the articles cited are out of date (i.e. [6, 7, 54) and should not be cited. In addition, the citations of some articles are incomplete and must be completed.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

All the issues raised were correctly addressed. Therefore, I support the publication in the present form.

Reviewer 2 Report

Authors have answered all the questions