Effect of Heat Input on Formability, Microstructure, and Properties of Al–7Si–0.6Mg Alloys Deposited by CMT-WAAM Process

Round 1

Reviewer 1 Report

Effect of heat input on formability, microstructure, 2 and properties of Al-7Si-0.6Mg alloys deposited by 3 CMT-WAAM process.

This study deals with the heat input effect during CMT-WAAM process in Al alloys deposition on their microstructure and mechanical properties. The subject of this study is of current research and industry interest and aligns well with the journal scope. In my view the manuscript should be further improved prior to be accepted.

Main points:

Abstract is not of sufficient and generally accepted quality of any research paper. The first sentence is not correct, since “In order to” requires connection to a result, such as alloy was manufactured. Thus, sentence 1 and 2 in the abstract should be combined. WAAM term was not yet introduced. What do you mean by stable mechanical properties? T6 heat transfer is not yet introduced. From the abstract it is not clear what the key point of the study is.

Introduction is rather confusing and not complete. There are many more recent studies and reviews on the WAAM deposited Al alloys. Also, with the focus on mechanical properties of Al-6Mg alloy, and their study provides similar values. Authors should specify why the Al-7Si-0.6mg was chosen, saying it is widely used is rather limited statement. The key points of WAAM and CMT-WAAM technologies of Al alloys manufacturing are not demonstrated, such as less material wastage, improved properties, etc. Also, the main drawbacks, such as porosity and residual stresses need to be discussed. The aim of theoretical support is not achieved at all.

 

From the results it looks that the wire feeding speed can significantly affect the deposited material, as demonstrated for sample #15. However, to achieve varying HI, the wire feeding speed was also varied from 5 to 6. This complicates the direct comparison.

Figure 10, 11 and 13 were taken with SEM or metallographic microscope? The Si, Fe phases should be confirmed using SEM-EDS with the map or at least point spectra. Figure 12, is the EDS data measured in a point or on entire map? Why no Ti?

One of the main issues in the deposited Al alloys in this method is porosity. The only three pictures in Fig.10 are clearly not enough. The authors should make stronger emphasis on measuring porosity and quantifying it, especially having excess to SEM. Thus, the statement about porosity is limited.

The mechanical properties need also more detailed studying. Only one each sample was studied. However, at least for #1,10 17, authors could have studied at least 3 independent samples to demonstrate error bars in Fig.14. The variation in properties is not that large. Moreover, authors should make attempt to elucidate porosity and residual stress effect on the measured mechanical properties.

 

Minor comments:

Table 1, how the values were obtained?

Figure 1, 2, 3, 9 are not necessary and should be moved to supplementary.

Line 84, the samples were etched.

What is average layer height?

Line 164, this sentence needs a reference.

UTS and YS should be explained.

Line 218, remarkable is not appropriate; especially such values were already reported for Al alloys.

Author Response

Thank you very much for your valuable Suggestions. I have made corresponding adjustments and explanations.Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

A nice paper, just a few comments:

Abstract:

L26-28, is a bit confusing, T6 is a strengthening heat treatment (precipitation) yet the authors then talk about heat input effecting grain size, this needs to be clarified. Also previously stating there was no anisotropy in the properties, and then stating heat input increases the anisotropy is contradictory (just needs to be written more clearly, e.g. little anisotropy in the mechanical properties is observed except at higher heat inputs).

Body:

L77 and L79, I assume “stretching sample” is meant to be “tensile sample”

Figure 14 could perhaps have error bars included to demonstrate the significance of the change in anisotropy that develops in the properties

Author Response

Thank you very much for your valuable comments. I have made corresponding adjustments and explanations. Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Effect of heat input on formability, microstructure, 2 and properties of Al-7Si-0.6Mg alloys deposited by CMT-WAAM process. 

The manuscript has been improved accordingly to most of the raised points. However, there are some confusing statements in the authors replay:

To point 3. “Of course, from the results, the WFS has a great influence on the forming of as-deposited WAAM Al-7Si-0.6Mg alloy (15#), and may also have an impact on the properties of the WAAM alloy. However, the results of this paper show that the WFS has no effect on the properties of WAAM alloy (T6).The influence of CMT-WAAM process parameters on the forming and properties of WAAM Al-7Si-0.6Mg alloy will be studied in another paper.”

First, authors have demonstrated results (#15) that WFS can significantly affect the forming process and the properties, and then authors claim that the result of this paper to show that there is no effect of WFS on the properties and then that process parameters effect will be studied in another paper. It is confusing

 

To point 5 “Response 5: In the detection of porosity defects, the authors observed multiple fields of view under each process condition. The results show that the pore size is mainly tens of microns, the distribution is uniform. The size and number of pores did not change significantly under different heat input conditions. This is mainly because Al-7Si-0.6Mg alloy has good fluidity. Previous studies have found that these micro pores have no effect on the macro mechanical properties. The metallographic pictures of low, medium and high heat input (1#, 10#, and 17#) are selected as the explanation. In the revised manuscript, SEM image of porosity is added to describe the shape and size of pores, and the description of pores is supplemented as follows:” .

The only one SEM image shows that the pore size is about 50 µm not tens of µm. There is not enough support to claim uniform distribution from the provided images. Also, the pore size variation in ± nm should be provided for a qualitative evaluation. Moreover, when authors use SEM to visualize and measure pore sizes, they will most likely find many much smaller size defects than 50 µm. The statements in the manuscript such as “The size and number of pores did not change significantly with the increase of heat input. Furthermore, the micro pores in the WAAM alloy have no effect on the macro mechanical properties [19]”  should be avoided since they are most likely wrong. The size and amount are not quantified and the claim about no effect of micro and other size pores on the macro mechanical properties just is a contradiction to physics and contact mechanics in general. I would suggest that such “effect” should be strongly linked to the amount of pores and their distribution, which again was not quantified.

Author Response

Thank you very much for your valuable comments. I have made corresponding adjustments and explanations. And all of the changes have been highlighted in blue in the revised manuscript (Round 2). Please see the attachment.

Author Response File: Author Response.docx