Sol–Gel Silica Coatings for Corrosion Protection of Aluminum Parts Manufactured by Selective Laser Melting (SLM) Technology

Round 1

Reviewer 1 Report

The authors studied the sol-gel silica coatings for corrosion protection of aluminum parts manufactured with Selective Laser Melting (SLM) technology.

 There are several problems to be addressed:

 1.     There is no any description of the adhesion test results. The authors should describe their results in section 3.1.

2.     The paper contains many illustrations and a few descriptions of the obtained results. The authors should expand the results description.

3.     Figure 10 contain image of one specimen. This result is valid for a series of specimens or only for this particular specimen?

4.      The authors should include few references from “Coatings”.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

The authors in their work analyze the possibility of using sol-gel silica (silicon oxide) coatings to effectively protect various surfaces of aluminum alloys produced by Selective Laser Melting technology. They have studied two different aluminum alloys and evaluated different aspects of the coating, including its effectiveness as a corrosion protector. The introduction to the subject and the review of the state of the art is wide and depth. They explain in a general way many aspects of each experimental arrangement. In my opinion the analysis of the results is not deep and therefore the conclusions reached are very generic. The article should deepen the discussion of the results and consider the following aspects whose response and integration in the manuscript will serve to enrich it and thus make it suitable for publication

 

To authors

1.      If the gel was applied by a spray method which is not reported to be automated, how to ensure homogeneity of the applied film?

2.      Why the study was carried out on aluminum alloys? if these are known to be very resistant to corrosion. I would expect that for the duration of the test that the uncoated alloy would exhibit good corrosion resistance.

3.      What is the advantage of applying a Sol-gel silica film as a corrosion protector compared to the protection provided by a traditional paint film?

4.      Why they did not perform the corrosion test on the uncoated alloys in order to compare the corrosion progress between the coated and uncoated alloys?

5.      what can you comment on the results of the adhesion test, as this is not discussed in the manuscript.

6.      In the evaluation of resistance to thermal cycling, because the tests were performed at temperatures below zero? Why not test at elevated temperatures ~ 200°C, one would think that the application of this type of alloys would be more common at elevated temperatures than at sub-zero temperatures.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

 

Board comments,

This paper seems to be about the corrosion resistance increment of the laser additive manufactured aluminium alloy with the coating generation. This seems to be carried out with cheap and environmental friendly. The stability of these coatings seems correctly to be evaluated with diverse techniques.   The corrosion resistance seems also to be analysed with acceptable method. Although this looks like a good paper, this has a huge deficiencies on experimental setup, results and discussion, hampered the understanding of the document. This paper may be considered to published after being improvised with the next comments. 

 

The abstract should have some sentences about the advantages of the sol-gel and your results to focus the theme.  

In the line 90 "to passivate alloys of steel, aluminum, zinc and other metals [16]. Chromate conversion" you say that steel is passivated but this is impossible. I think that you wanted to say stainless steel.

The details of the milling process, laser additive manufacturing and optical light microscopy analyses should be added in the 2. Materials and Methods part to increase the understanding of you work. 

The next paragraph should be in 2. Materials and Methods part in 226-233line "Adhesion refers to the ability of a coating or paint to stick to a substrate or surface. 226 ASTM D3359-17 is a standard test method for measuring the adhesion of coatings to sub-strates. It is commonly used in the paint and coating industry to evaluate the quality and 228 durability of coatings on a variety of substrates. The ASTM D3359-17 test method involves applying a grid pattern on the coating sur-face with a cutting tool, and then applying a adhesive tape over the grid pattern. The tape is then removed quickly at a 90-degree angle to the surface, and the amount of coating that remains on the surface is evaluated based on the grid pattern (Figure 9). " 259-273 lines "The Neutral Salt Spray Test is a test method used to evaluate the corrosion resistance of materials and coatings. MIL-STD-810G w/change 1 Method 509.6 is the standard that was used and specifies the procedures for conducting the Neutral Salt Spray Test. The test involves exposing the test specimen, which can be a material or a coated surface, to a salt spray mist in a controlled environment for a set period of time. The salt spray mist was composed of a 5% sodium chloride solution. 264 These are the parameters used for the test:  (a) 24 h of salt spray (T 35°C, pH 7,0) 266 (b) 24 h under drying conditions @23°C +/-5C° & humidity of 50 %UR +/-10 %UR 267 (c) 24 h salt spray (T 35°C, pH 7,0)  (d) 24 h under drying conditions @23°C +/-5C° & humidity of 50 %UR +/-10 %UR  During the test, the specimen is inspected periodically to assess the extent of corrosion or damage to the surface. Specimens used for test had a part of surface raw and a part milled, test results show" 279-300 lines "The determination of thermal cycling resistance is a test method used to evaluate the ability of a material or product to withstand changes in temperature over time. This test method is important in determining the durability and reliability of coating that will be exposed to temperature changes during their lifetime. The following thermal conditioning was performed: 283 Repetition for 5 times of the first cycle: • Ramp of 1 hour down to the temperature of - 54°C 285 • Maintaining the temperature of - 54°C for 3 hours 286 • Ramp of 1 hour up to the temperature of 23°C 287 • Maintaining of the temperature of 23°C for 10 minutes 288 289 Repetition for 5 times of the second cycle: 290 • Ramp of 1 hour down to the temperature of - 110°C 291 • Maintaining the temperature of -110°C for 3 minutes. • Ramp of 1 hour up to the temperature of 23°C 293 • Maintaining the temperature of 23°C for 3 hours  During the test, the test specimen is monitored for any changes or damage that may occur as a result of the temperature changes. This can include cracking, delamination, or other forms of physical or chemical degradation. Specimens used for test had a part of surface raw and a part milled, test results show no defects on treated surfaces as visible in Figure 11 (left before test, right after test)" because these are experimental conditions.

The result discussion of the testing are poor, the explanations on the features of the materials are absent. This does impossible the understanding of the work.

Specific comments

The specific comments are the following:

To add reference in line 39 "computer systems (e.g., vision systems, robotic systems, etc.) [REF]." 

To include reference in line 42 "of new customers resulting from the globalization of markets [REF]."

To incorporate in reference line 69 "sustainability [REF]."

To add reference in line 74 "ower energy consumption and thus less air pollution [REF]. "

To include reference in line 77 "arge microstructure [REF]. Conversely, parts produced by SLM technology have a very fine"

To incorporate in reference line 106 "in the case of AM technology can be atomized into powders for use with SLM technology [REF]."

To add reference in line 158 "9227 [REF]. In addition to the salt spray test, further tests were carried out to verify corrosion" 

To incorporate reference in line 162 " Adhesion – ASTM d3359-17 [REF]"

To add reference in line 175 "to ISO 9227 [REF] with 168 hours of continuous exposure) of the sol-gel silica-based coating"

To incorporate reference in line 218 "originate in the underlying metal; so the corrosion protection function is effective [REF]."

The Selective Laser Melting should be replaced by selective laser melting in line 23 and 27

To replace Chromate by chromate in line 96  

 

 

 

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The paper can be accepred in present form

Author Response

Thank you again for your comments. We have revised the manuscript slightly. In the manuscript, changes are highlighted in green (previous changes were left in yellow).

Reviewer 2 Report

The authors adequately addressed the recommendations made to improve their manuscript.

Author Response

Thank you again for your comments. We have revised the manuscript slightly. In the manuscript, changes are highlighted in green (previous changes were left in yellow).

Reviewer 3 Report

Board comments,

This paper is a study about the corrosion resistance increment of the laser additive manufactured aluminium alloys with the coating generation. This was carried out with cheap and environmental friendly. The stability of these coatings were correctly evaluated with diverse techniques.   The corrosion resistance was also analysed with acceptable method.  This paper can thus be published after replying  with the next comments. 

The suppliers of the laser device and the metallic powders should be added in 2. Materials and Methods part because indicating  a good suppliers.

The wavelength of the laser should be indicated in 2. Materials and Methods part due to this modifies the laser radiation behaviour with the material. 

The standard should be referred to be able consulted by the readers. 

Specific Comments,

My specific comments are the following;

To add reference in line 262 "alloy having lighter coloration characterized by a different light diffusion property [REF]."

To incorporate reference in line 276 "coating was added with functionalizing elements to increase heat transfer [REF]"

To included reference in line 290 "triggers a more localized beginning of the corrosion [REF]. Analogously the Al6061 surface is"

To add reference in line 293 "of fabricated surfaces [REF]."

To include reference in line 317 "tension gradient [REF]. Between the bumps some salt deposits were trapped without altering"

To add reference in line 321 "also, light small area are salt crystals incorporated in the bumpy surface [REF]. Total different"

To incorporate reference in line 329 "intermediates of the elements composing the alloy [REF]."

 

To included reference in line 340 "may cause damages which are classified according to the standardized method [REF]. The re-"

The VED acronym of the line 391 "The as is Al6061 shows a better surface finishing due to the higher VED which leads to a" should previously be defined.

To add reference in line 405 "iability is observed for as is Al6061 without outliers [REF]. "

To incorporate reference in line 442 "and contraction of molecular bonds which leads to cracking and early failure [REF]. Rapid"

 

 

 

 

Author Response

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Author Response File: Author Response.docx