Effects of Ni and Co on the Corrosion Resistance of Al-Si-Cu-Zn-Fe Alloys in NaCl Solution

Round 1

Reviewer 1 Report

The paper is well and clearly presented. 
My main concern is the interpretation of the  EIS results: you refer to [23] to justify this choice of potential for EIS after 1 hour immersion.
In [23] Mansfeld have the same EIS plots at OCP and -20mV OCP after 3 days of immersion but not after 1 hour.
Are you sure that the EIS plots at -20mV OCP  after 1 hour are representative your interpretations on corrosion as your experiments are in a cathodic zone of the potentetial? Can you explain?

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The paper is very nice, can be accepted for publication

Author Response

We appreciated the Reviewer's comments.

Reviewer 3 Report

In present study "Corrosion resistance of Fe-contaminated Al-Si-Cu-Zn alloys modified with Ni and Co and with variable secondary dendrite arm spacing" the corrosion behavior of Fe-bearing directionally solidified  and centrifugally cast Al-Si-Cu-Zn-based alloys doped with Co or Ni  has been investigated. The paper corresponds well to the journal scope. The data is well designed and reported. The achieved results are novel and of a noticable scinetific value. I suggest the present research can be published in present state.  

Author Response

We appreciated the Reviewer's comments.

Reviewer 4 Report

1) Dear authors, the title should reflect the essence of the work, while in your case, the title does not correspond to what is happening in the article. The basis of the alloy is the Al-7Si alloy, although the Al-Si-Cu-Zn system appears in the title and annotation. However, you consider Cu and Zn additions as impurities. What method was used to determine the compositions of the obtained alloys?
2) Introduction requires processing. Why was this alloy composition chosen? Why were these modes of obtaining the alloy applied? How is it different from previous work in this area? It is well known that nickel improves corrosion properties. What is the novelty of the work?
3) The technique for obtaining the alloy requires additional discussion. What is the reason for holding at a temperature of 800 for 40 minutes? Why was this temperature chosen? The liquidus of this alloy is about 650. « The electrical ca- 123 ble was unplugged after the nearest thermocouple from the cooled base indicated 5% 124 above the alloy liquidus temperature. Thermal analysis was previously used to establish 125 the liquidus temperatures." what is this study?
4) “The samples were chosen to focus on the variance of Fe-containing intermetallics un- 135 der slow and fast solidification regimes: SDAS of approximately 21 m for the DS samples 136 and of approximately 5 m for the CC samples of the three alloys. Other features within 137 each kind of processing, such as the Si spacing, which correspondingly follows the SDAS 138 size as shown schematically in Figure 1, were examined, and may be regarded constant. 139 For alloys within each processing, the intermetallic proportion remained almost constant. 140 When comparing the differences across processing methods, a difference in the length- 141 scale of the phases may be seen as will be discussed later"
Please provide further explanation. Add images on which these calculations were made.
5) Please explain why the concentrations of Cu and Zn alloying elements (you call them impurities here) are lower than declared in the alloy?
6) “After cleaning, the samples were weighed to be compared to the masses before…..This is consistent with what is reported in the current 363 study when the results through the electrochemical and the 30-day immersion tests are 364 compared to each other." Please explain further this paragraph. Why is there an increase in mass? Why is the corrosion rate at the initial moment (1-3 days) for an alloy with Ni higher than for the others, but according to the results of a 30-day test, the corrosion rate turned out to be negative?
7) Why was the introduction of additional elements Cu and Zn at all, if their influence is not evaluated in any way.
8) Conclusions are required to be rewritten on the basis of the work done.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

In this revision you do not remove your interpretation of EIS results / corrosion or validate them by examination of yours samples as in papers [26-28].

I agree that the EIS response when performed at Ecorr can not be linear: so you performed the EIS at Ecorr -20 mV after 1 hour of immersion. In [25] Mansfeld have the same EIS plots at OCP and -20mV OCP after 3 days of immersion but not after 1 hour.

From your only EIS results at -20 mV/OCP you can not give trends and conclusion on the corrosion speeds.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

Dear authors, thank you for answering my boring remarks.
However, a number of additional questions still remained unsolved:
1) We have established the need for the presence of elements Zn and Cu in alloys. But these elements, as shown in Figure 3, are much less in your alloys. Points b1, a1, b2, a2, b3, a3 correspond to a solid solution of aluminum and indicate that the concentrations are much lower. please explain why is this so?
2) Also, in Figure 3, the signature indicates the concentration in atomic percent, when you specify mass percent in the experimental procedure. What data is correct?
3) The methodological question about the exposure of 40 minutes was not asked by chance. Since Zn is fusible, and at a given exposure, most of it can burn out.
4) In the conclusions, the use of such revolutions is not good "Ecorr clearly demonstrates that the icorr is more likely to be found at better levels ranging from 10-6 to 10-5 A/cm2"

Author Response

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Round 3

Reviewer 1 Report

I accepted the second revision of the paper

Author Response

Thanks for tour comments.

Reviewer 4 Report

1) Еhe concentrations in these alloys are very different from those declared by the authors with respect to Zn and Cu. If the concentration of Cu is possibly close to the declared one, the concentration of Zn does not exceed 0.1%.
2) It is not clear why the concentrations in mass percent are the same as the concentrations in atomic percent.

Author Response

We already answer these questions in the last set of responses.