Percolation of Primary Crystals in Cell Walls of Aluminum Alloy Foam via Semi-Solid Route
Round 1
Reviewer 1 Report
The authors investigated the stabilization mechanism of aluminium alloy foams obtained by a semi-solid route that employs primary crystals to increase the stabilization.
The manuscript is on an interesting topic but they do not carry out a sufficiently deep characterization of the materials to obtain good results. I suggest some changes to improve the manuscript.
The inclusion of some recent articles would be useful to provide the readers with a state of art that help to better understand the problematic and the contribution of the research presented here.
Line 47. It depends also of other factors such as de size of pores and the homogeneity in their distribution (see eg. Zhou et al., 2020) and references therein.
Gil, R., Kennedy, A. R. (2012). Capillarity-driven infiltration of alumina foams with an al-mg alloy: Processing, microstructure, and properties. Journal of materials engineering and performance, 21(5), 714-720.
Jinnapat, A., Kennedy, A. (2011). The manufacture and characterisation of aluminium foams made by investment casting using dissolvable spherical sodium chloride bead preforms. Metals, 1(1), 49-64.
Zhou, X., Li, Y., Chen, X. (2020). Development of AlMg35-TiH2 Composite Foaming Agent and Fabrication of Small Pore Size Aluminium Foams. Journal of Materials Processing Technology, 116698.
Line 77-78. These are conclusions, then they should not be here.
Line 89-91. Tables 1 and 2 could be in one merged table.
Si from table 2 need two decimals.
Line 94. “The master aluminium alloy was 94 completely melted in the electronic furnace in air”. Please can you indicate at which temperature did you arrived?
Lin 99 why till 615 ºC exactly?
Why you did not any Dilatometry thermal analysis (DTA) or differential scanning calorimetry (DSC)?. These should give you important data on the nucleation and crystallization that could be useful to the best thermal treatment to obtain the maximal number and smallest size of crystals.
Line 170. A porosimetry analisys also should be very useful here (see eg. Jinnapat and Kennedy, 2011; Gil and Kennedy, 2012).
Line 181. The observation of crystals need an observation in a small scale eg. Using a SScanning electron microscope. In images of your Figure 8 we only can observe a mass but we cannot observe the texture of crystals (see eg. In Jinnapat and Kennedy, 2011).
The discussion is interesting but it is limited by the poor methods to obtain the data.
The section of conclusions must be improved. The first conclusion should be rewritten.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Dear Authors,
The manuscript is very interesting for the publication in the Metals, however I have a few comments for the author:
Line 47: Please mark the reference when stating ‘The volume fraction of the particles in metal foams should be in the range of 5-15%.'
Line 82, 83: use wt.% instead mass%, the same in Table 1 and 2 and line 102, 111
Line 84: correct 8.3 s−1 to 8.3 s−1
Line 85: Use space after Ï•
Line 101: use space when writing (100×100 mm2)
Line 115: …. foam was cut into in half through the center. Correct into …. foam was cut in half through the center.
Line 128: Am should be explained in more detail.
Line 144: When describing used equipment, you should write also the state of manufacturer. The same line 145.
Line 171: ρnp of 2.67 x 103 kg/m3. Correct!
Line 172: equivalent pore diameter , …. use Math type through all the text! (line 179, 220, 223, …) An variable should be written italic.
Line 191: Mark the reference at the end of the sentence: This value is two times higher than the set solid fraction of 12%.
Line 224: Reference [5] in text is not marked correct.
Line 259: Kuwahara et al. … Ref. No. is missing
Fig. 11 and 12: Check the colouring marks of the phases.
All Equations should be written in Math type!
Ref. [3] and [15] after the authors delete ;.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The manuscript sets out to investigate the stabilization mechanism of cell walls in an aluminum alloy foam formed by the semi-solid route employing primary crystals as a thickening agent. Microscopic images were analyzed to determine bubble and primary crystal size and positions. Aggregated crystals in the plateau border clogged the film drainage, and a 2 dimensional percolation model was used to show film drainage was impaired even in regions deplete of crystals. The assessment was unchanged following consideration of flow restrictions in a 3 dimensional foam. The conclusions reached by the authors regarding the stabilizing effect of the primary crystals and their aggregates are reasonable. This reviewer recommends the manuscript be published without modification.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
All the suggested corrections have been introduced or convincingly, argued in the response file. I consider that the manuscript is now correct and ready to be accepted.
