Investigation of the Mesoscale Damage Evolution Process of AA5754O Aluminum Alloy CMT Welded Joints

Round 1

Reviewer 1 Report

I am of the opinion that the main topic of this paper is novel and potentially interesting for the research community. Quantified data on the evolution of defect numbers and sizes can be valuable for calibration or validation of numerical damage models. A major point of concern, however, is the statistical relevance of the reported data.

Significant language editing will be needed to improve the readability of the paper. Some details of technical aspects and their discussion should also be improved. Hereunder I provide a list of comments/suggestions/questions that should be considered by the authors.

- line 40 (and others): 'condensation' to be replaced by 'solidification'
- line 42: FZ, HAZ - abbreviations should be explained at their first use
- line 50: mismatching characteristics -> define which type of characteristics
- line 53: 'at different positions' is not a clear statement
- line 55: the authors use reference 12 to support a statement about the effect of CMT welding on microstructure, whilst that reference deals with friction stir welding
- line 58: similar comment with respect to references 13,14
- line 64: five references are added for a general statement; these could be limited to the most appropriate ones for metal alloys. In my opinion a more in-depth discussion on the use of CT for the characterisation and quantification of damage in metal alloys should be added to this introduction as that is the most important scientific topic of the paper.
- line 66: 'finite element simulation of welded joints' is not a sufficiently accurate description (I suppose the authors refer to damage modelling)
- line 70: 'tissue' is not the appropriate word
- section 2.1: More information on the welding process is needed: heat input, filler wire diameter, filler wire feed rate, cleaning of the plate before welding
- figure 1 has no added value; figure 2 (and several others) should contain an indication of dimensions or a scale bar
- section 2.3, line 108: the indentation width is not important, the weight used for hardness testing should be mentioned
- section 2.4: It is not clear how many tensile tests have been performed for both HAZ and FZ; I would expect at least 3 to allow quantification of mean values and their ranges. The text does not discuss the specimen thickness; was the original shape of the weld kept intact or was it ground flush with the plate surface?
- line 135 and following: More information on software settings is needed to know the accuracy and resolution of the scans (eg., it is not clear to what volume 20 voxels coresponds). I don't understand the phrase 'the evolution behavior of defect removal'. 
- figure 5 is pixelated (also others); add the numbers of the scanning points to both curves
- line 150: I don't understand the phrase 'the welding effect is good'
- line 154 and following: this discussion can be improved. Reference 20 concerns another aluminium alloy. I recommend the authors to determine the actual phases for the welds made in this work.
- figure 7 is of too low quality to allow visual analysis of the microstructure, base metal should also be identified
- line 171: I don't know the expression 'floating speed of the molten pool'
- sections 3.2-3.4: Are these based on one single specimen for HAZ and FZ? In my opinion this should be based on at least 3 observations to take account for the variability of weld quality. 
- section 3.2: How did the authors ensure that at all stages the volume of inspected material corresponded to the original volume inspected at the initial stage? Did you also scan some base material and compared these to scanned images of the HAZ and FZ initial stages. Two different colours are used on figures 10 and 11; their meaning should be explained in the text or figure captions.
- line 194 (and others): what is 'polymerization behavior'?
- line 201: The authors mention that the average sphericity will decrease with accumulation of strain. It could be briefly explained why this is the case.
- line 218: what is meant with 'certain characteristics of layered distribution'?
- section 3.3: defects are characterized in bins of 4 micrometer (haz) or 10 micrometer (fz); is there any motivation to select these numbers?
- line 239-240: I don't understand what is meant with 'the tensile equivalent diameter of the specimen'.
- caption of figure 13 is not correct
- section 3.3: is it possible to quantify the nucleation rate of defects?
- section 3.4: I am not convinced of the quality of the Rice and Tracey fit on figure 15. Did the authors quantify the goodness-of-fit by means of any statistical metric?
- equations 3.3 and 3.4: parameter T is not defined; what is the value of alfa_RT?, how is dN calculated?
- line 283: I don't understand the phrase 'insufficient number of experiments for the initial minimization problem'.
- line 286: reference 27 is about dual phase steel; what is its relevance for this part of the text?
- section 4: I am of the opinion that the conclusions should be written more concretely and contain quantification.
- This work focuses on defect nucleation and growth. For damage modelling also defect coalescence is of importance; can this be discussed based on the observations reported in this paper?

Author Response

Dear reviewer.
Thank you for your advice. According to your suggestion, the author has modified the article. Please see the attachment for the specific reply.

Kind regards,

Wenyuan Kang
Nanjing University of Science and Technology

Author Response File: Author Response.pdf

Reviewer 2 Report

The author presented "Investigation of the meso scale damage evolution process of the 2 AA5754O aluminum alloy CMT welded joint", the tensile behavior, hardness evolution and microstrucutre through metallography are presetented. The paper is interesting and presented some novel approches to fabricate AA5754O. there are some minor concerns with the manuscipt
1. introduction, introduce CMT so that early stage reaserchers can understand the term completely
2. Abstract needs to be modify in terms of tensile, hardness etc.,
3. line 24 and 25 needs to re-write again.
4. line 44, ductile fracture?????
5. gap of the study is well prestented, needs to introduce HAZ and FZ in introduction at their first use.
6. line 86, (shown in Fig. 1.The), needs space after Fig. 1., similarly after table. 2. in following line "ters are shown in Table 2,the"

7. the wire cutting technology????? please write technical words
8. line 96, (ints. And then the cut) , the sentence can not start with the word "And"
9. line 104-105 are prolonged, short it
10. Most of the time sentence started with "in order to", avoid to many repetitions
11. Fig. 5 and Fig. 6 axial font size should be same

12. The HAZ is 157 mainly composed of α Solid solution and dispersion distribution β (Al3Mg2) phase.???? how to identifity by OM image.
13. in depth analysis is missing, rest paper is well written
14. Conclusion is well written and it should be introduce in the abstract section as well.

Author Response

Dear Reviewer

Thank you for your advice. The author has modified the content of the article according to the reviewer's suggestion. Please see the attachment for the reply.

Kind regards,
Wenyuan Kang

Author Response File: Author Response.pdf

Reviewer 3 Report

This manuscript presents an experimental investigation on the damage evolution process of the 2 AA5754O aluminum alloy welded joint. The authors have reported detailed experimental investigations. The experimental approaches used are sound. The only concern is the original contribution of the current paper. All the experimental methods have been well established. There is no novelty in the experimental methods. In addition, the modified R and T model has also been reported by other researchers. 

Author Response

Dear Reviewer

Thank you for your advice. As suggested by the reviewer, the authors will conduct further research on the damage behavior of aluminum alloy CMT welded joints. At the same time, the author believes that although other scholars have used CT to analyze the evolutionary behavior of aluminum alloys, yet very few researchers had used CT to study the damage evolutionary behavior and reveal the processes of aluminum alloy CMT welded joints. In this paper, the damage evolution behaviors in fusion zone and heat affected zone of CMT welded joints were characterized respectively, and the damage evolution behaviors in different areas of CMT welded joints were observed, which is an original contribution in this domain.

Kind regards,
Wenyuan Kang

 

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

The authors have addressed the concerns raised. The paper is now acceptable.

Author Response

We would like to thank the reviewers for taking the time to read through our manuscript and provide detailed comments。