Optimization of Parameters in Multi-Spot Projection Welding of Thin Aluminized Steel Sheets

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors studied the effects of different projection welding parameters on the microstructure and mechanical properties of thin aluminized steel sheets. The topic is relevant, but the manuscript would benefit from substantial improvements in logic, structure, and clarity. My detailed comments are as follows:

1. The importance of projection welding is mentioned, but the literature review is presented in a rather scattered way, without clear focus. At present, the challenges of projection welding for thin aluminized low-carbon steel sheets and the corresponding industrial application scenarios are not clearly highlighted. It is suggested that the authors reorganize the introduction to emphasize the novelty and practical value of the study.
2. In Section 2.1, the reported mechanical properties of the base material (yield strength, tensile strength, and elongation) appear much lower than the typical values for low-carbon steels. The authors are encouraged to carefully recheck and clarify this part.
3. The experimental section lacks some essential details. For instance, how were the thicknesses of the sheets and the welding time ranges selected? Please provide a clearer explanation of the criteria or references used.
4. The manuscript structure could be improved for better clarity. For example, why are Sections 3.1 (Welding process) and 3.2 (ANOVA and Taguchi-based DoE) presented under the results part? In addition, Section 3.3 (Microstructure) still contains descriptions of sample preparation, which would normally belong to the experimental section. Similarly, Figure 5a is placed in Section 3.3, while its description appears later in Section 4.1. A thorough reorganization is recommended.
5. In the microstructural analysis, the authors presented the base material (Figures 4 and 5) and an isolated welded sample (Figure 6). However, this part provides limited useful information and seems somewhat disconnected from the main research focus. Readers would be more interested in a comparative analysis of microstructures under different welding parameters, which is unfortunately missing.
6. The authors claim that interdendritic cracks occur at higher welding power but no micro-cracks are found at lower power. However, the field of view in Figure 9 is too limited to properly observe and compare the overall crack distribution in the weld zone. Broader and more representative images are needed.
7. The arrangement of figures and equations needs significant improvement to ensure clarity. For example, the sub-figures in Figure 1(a) and (b) are not aligned; Figures 4 and 5 contain two overlapping scale bars, and spacing is inconsistent; Figure 6 lacks alignment and scale bars. Careful formatting is recommended.

Author Response

R1. Open Review

Comments and Suggestions for Authors

The authors studied the effects of different projection welding parameters on the microstructure and mechanical properties of thin aluminized steel sheets. The topic is relevant, but the manuscript would benefit from substantial improvements in logic, structure, and clarity. My detailed comments are as follows:

1. The importance of projection welding is mentioned, but the literature review is presented in a rather scattered way, without clear focus. At present, the challenges of projection welding for thin aluminized low-carbon steel sheets and the corresponding industrial application scenarios are not clearly highlighted. It is suggested that the authors reorganize the introduction to emphasize the novelty and practical value of the study.

1. Thank you for this valuable comment.

Continuous improvements in the aluminizing process have expanded the possible applications of steel components coated with thin layers of Al or Al-Si alloys. Such semi-finished products are often found in the manufacture of components for the automotive industry or in the production of baking molds for the food industry. Since many aluminized steel components are welded, it is important to know the phenomena occurring in the molten core area, which affects the strength characteristics of the joints. Currently, few references in specialized literature have addressed this issue.

1. In Section 2.1, the reported mechanical properties of the base material (yield strength, tensile strength, and elongation) appear much lower than the typical values for low-carbon steels. The authors are encouraged to carefully recheck and clarify this part.

1. Thank you for alerting us to this issue. Indeed, we only included the lower limit value for tensile strength. The quality certificate indicates a value of 161 MPa for this mechanical characteristic, so we have corrected this in the manuscript.

1. The experimental section lacks some essential details. For instance, how were the thicknesses of the sheets and the welding time ranges selected? Please provide a clearer explanation of the criteria or references used.

1. You are right, I did not provide details on these aspects in order not to complicate the manuscript too much.

We chose the thicknesses of the welded sheets based on a practical application in the factory. One of the authors, who is a PhD student, works in a factory that produces baking molds for the food industry and encountered problems related to the strength of the welds on aluminized steel semi-finished products. Therefore, the combination of thicknesses like that in production was chosen, and the values ​​of the welding parameters were chosen based on a study carried out on several batches of welded products, which were tested to failure.

1. The manuscript structure could be improved for better clarity. For example, why are Sections 3.1 (Welding process) and 3.2 (ANOVA and Taguchi-based DoE) presented under the results part? In addition, Section 3.3 (Microstructure) still contains descriptions of sample preparation, which would normally belong to the experimental section. Similarly, Figure 5a is placed in Section 3.3, while its description appears later in Section 4.1. A thorough reorganization is recommended.

1. You are right about this, which is why we have corrected and reorganized the text.

1. In the microstructural analysis, the authors presented the base material (Figures 4 and 5) and an isolated welded sample (Figure 6). However, this part provides limited useful information and seems somewhat disconnected from the main research focus. Readers would be more interested in a comparative analysis of microstructures under different welding parameters, which is unfortunately missing.

1. We agree with your observation. To better highlight the distribution of elements through the interface between the Al-Si protective layer and steel, we have included in Fig. 6 another image (element distribution line).

1. The authors claim that interdendritic cracks occur at higher welding power, but no micro-cracks are found at lower power. However, the field of view in Figure 9 is too limited to properly observe and compare the overall crack distribution in the weld zone. Broader and more representative images are needed.

1. You are right, we add another image with visible interdendritic cracks (Fig. 9).

1. The arrangement of figures and equations needs significant improvement to ensure clarity. For example, the sub-figures in Figure 1(a) and (b) are not aligned; Figures 4 and 5 contain two overlapping scale bars, and spacing is inconsistent; Figure 6 lacks alignment and scale bars. Careful formatting is recommended.

1. We totally agree with your observations and suggestions, and we modified and added some figures (Fig. 5, Fig. 6, Fig. 9, Fig. 10, Fig.11).

We would like to thank the reviewer for the valuable feedback. The changes in the manuscript have been achieved by reorganizing the parts for better clarity.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Authors study the effect of the process parameters during multi-point projection welding on the tensile strength of the joints between aluminized steel components. Taguchi method was used to optimize the values of the welding process parameters and through the use of ANOVA method and detailed SEM-EDS analysis of weld cross-sections and tensile testing, it was shown that for the same set of welding parameters, joint breaking force is largely dependent on the number of protrusions. The work is explicit however, the author finds that there is no clear novelty in the study. Purpose and impact of the work is not clear, especially in the introduction section. The paper may therefore be rejected in the present form.

The following are the detailed comments from the reviewer:  

1. What is the main question addressed by the research?

  Ans. The paper intends to study the effects of the process parameters during multi-point projection welding focussing on correlation of microstructural evolution, especially that of intermetallic particles on the tensile strength of the joints aluminized steel components with varying protrusions.  

2. What parts do you consider original or relevant to the field? What specific gap in the field does the paper address?  

Ans. Optimization of process parameters (as the authors did, using ANOVA) and detailed microstructural characterization of intermetallic particles at the edge of the welded points is critical to define the mechanical properties of the welded joints and is very important in the field of multi-projection welding. However, the poor quality of data analysis and the presentation in the paper makes it difficult to understand exactly the gap that the paper tends to address.  

3. What does it add to the subject area compared with other published material?  

Ans. The reviewer feels that the paper does not add any new understanding in the field as because while reading the results and discussion and conclusions section, there is no correlation of the cross-sectional SEM analysis including that of EDS results of aluminized layer on steel substrate with the mechanical properties of the welded points. Also, there is no mention of any intermetallic particle (in the conclusions) that the paper initally aimed to study in the welded parts. Unless, such issues are addressed, the paper does not add anything important compared to the already published respots  

4. What specific improvements should the authors consider regarding the methodology?  

Ans. The reviewers' suggestion to the authors is to consider focussing on the combined importance of microstructural evolution  of intermetallic particles (IMP) and number of protrusions on the mechanical properties of the welded joints. Authors may use high-end characterization tools e.g. TEM and APT to clearly understand the evolution of IMPs.   5. Are the conclusions consistent with the evidence and arguments presented?   Ans. In the conclusions section, the present focus is primarily on the effects of # of protrusions in welded parts and parameter optimization (through ANOVA) on the breaking force with no mention of anything related to the microstructural evolution of the welded components. So the reviewer feels that conclusions needs to be more in line with explaining the origin of varying breaking force with # of protrusions which can only be addressed through systematic microstructure evolution.   6. Are the references appropriate?   Ans. Considering the present form of the manuscript, the references look fine   7. Any additional comments on the tables and figures and the quality of the data.   Ans. The overall quality of figures and data (especially that of SEM images) is extremely poor. Few SEM images are scratchy (Fig. 9). In some, scale bars and EDS spot labels are not visible (Figs. 5 and 6). The English language is also of extremely poor quality.  

Comments for author File: Comments.pdf

Author Response

R2. Open Review

Authors study the effect of the process parameters during multi-point projection welding on the tensile strength of the joints between aluminized steel components. Taguchi method was used to optimize the values of the welding process parameters and through the use of ANOVA method and detailed SEM-EDS analysis of weld cross-sections and tensile testing, it was shown that for the same set of welding parameters, joint breaking force is largely dependent on the number of protrusions. The work is explicit however, the author finds that there is no clear novelty in the study. Purpose and impact of the work is not clear, especially in the introduction section. The paper may therefore be rejected in the present form.

The following are the detailed comments from the reviewer:  

1. What is the main question addressed by the research?

  Ans. The paper intends to study the effects of the process parameters during multi-point projection welding focussing on correlation of microstructural evolution, especially that of intermetallic particles on the tensile strength of the joints aluminized steel components with varying protrusions.  

1. What parts do you consider original or relevant to the field? What specific gap in the field does the paper address?  

Ans. Optimization of process parameters (as the authors did, using ANOVA) and detailed microstructural characterization of intermetallic particles at the edge of the welded points is critical to define the mechanical properties of the welded joints and is very important in the field of multi-projection welding. However, the poor quality of data analysis and the presentation in the paper makes it difficult to understand exactly the gap that the paper tends to address.  

1. What does it add to the subject area compared with other published material?  

Ans. The reviewer feels that the paper does not add any new understanding in the field as because while reading the results and discussion and conclusions section, there is no correlation of the cross-sectional SEM analysis including that of EDS results of aluminized layer on steel substrate with the mechanical properties of the welded points. Also, there is no mention of any intermetallic particle (in the conclusions) that the paper initally aimed to study in the welded parts. Unless, such issues are addressed, the paper does not add anything important compared to the already published respots  

1. What specific improvements should the authors consider regarding the methodology?  

Ans. The reviewers' suggestion to the authors is to consider focussing on the combined importance of microstructural evolution of intermetallic particles (IMP) and number of protrusions on the mechanical properties of the welded joints. Authors may use high-end characterization tools e.g. TEM and APT to clearly understand the evolution of IMPs.  

5. Are the conclusions consistent with the evidence and arguments presented?  

Ans. In the conclusions section, the present focus is primarily on the effects of # of protrusions in welded parts and parameter optimization (through ANOVA) on the breaking force with no mention of anything related to the microstructural evolution of the welded components. So the reviewer feels that conclusions needs to be more in line with explaining the origin of varying breaking force with # of protrusions which can only be addressed through systematic microstructure evolution.  

6. Are the references appropriate?  

 Ans. Considering the present form of the manuscript, the references look fine  

7. Any additional comments on the tables and figures and the quality of the data.  

Ans. The overall quality of figures and data (especially that of SEM images) is extremely poor. Few SEM images are scratchy (Fig. 9). In some, scale bars and EDS spot labels are not visible (Figs. 5 and 6). The English language is also of extremely poor quality.  
peer-review-49671639.v1.pdf

R: We would like to thank the reviewer for the valuable feedback. The ANOVA analysis of welding parameters provides important insights regarding the statistical significance and effect of various welding parameters on the resulted weld characteristics (maximum breaking force and displacement at break) and can provide the contribution of each parameter to the variance in the response, showing which factor is most impactful. Moreover, it supports the statistical response for the prediction of weld outcomes.

 To clarify this aspect, more explanations are provided in the manuscript.

Based on your objective and critical analysis, we have made several improvements to the content, the quality of the figures, and the English translation. Two more bibliographic references have been added, and the text has been restructured. All changes made are underlined in red text.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript focuses on parameter optimization for multi-spot projection welding of thin aluminized steel sheets, a topic with high industrial relevance—especially for automotive lightweighting and other fields where joining coated steel components is critical. Its research methodology is systematic and rigorous. I think the following questions should be considered:
1. The manuscript identifies optimal welding parameters via the Taguchi method but does not conduct validation tests. Without fabricating samples using these "optimal" parameters and verifying their mechanical performance, the reliability of the optimization conclusions is weakened.
2. While it notes that 5-protrusion samples have higher elongation but similar breaking force to 3-protrusion samples, the underlying mechanism is underdeveloped. The claim of "current streamline dissipation" is overly superficial, lacking support.
3. The abstract and discussion mention "formation of intermetallic compounds" but fail to specify IMC types or quantify their content/distribution. This gap limits understanding of how IMCs influence joint brittleness or strength.
4. The scale bar in Fig. 6 are missing.
5. Where is the EDS results in Fig. 5b?

Author Response

R3

Open Review

Comments and Suggestions for Authors

The manuscript focuses on parameter optimization for multi-spot projection welding of thin aluminized steel sheets, a topic with high industrial relevance—especially for automotive lightweighting and other fields where joining coated steel components is critical. Its research methodology is systematic and rigorous. I think the following questions should be considered:
1. The manuscript identifies optimal welding parameters via the Taguchi method but does not conduct validation tests. Without fabricating samples using these "optimal" parameters and verifying their mechanical performance, the reliability of the optimization conclusions is weakened.

1. We would like to thank you for the valuable feedback. We appreciate the point regarding the importance of validation tests to confirm the reliability of the optimal welding parameters. The next plan is to conduct a larger set of experimental validation to fully verify the optimization results, and to present in further works. We have introduced this explanation in the revised manuscript to acknowledge the need for further validation.
2. 
   While it notes that 5-protrusion samples have higher elongation but similar breaking force to 3-protrusion samples, the underlying mechanism is underdeveloped. The claim of "current streamline dissipation" is overly superficial, lacking support.
3. Samples with 5 protrusions have a higher elongation at break because there are more bonding points that must yield before the sample breaks.
4. 
   The abstract and discussion mention "formation of intermetallic compounds" but fail to specify IMC types or quantify their content/distribution. This gap limits understanding of how IMCs influence joint brittleness or strength.
5. Thank you for this valuable suggestion. I have added text to the manuscript and described the effect of intermetallic compounds.
   4. The scale bar in Fig. 6 are missing.
6. We’ve changed the figure 6.
   5. Where is the EDS results in Fig. 5b?
7. We’ve added the figure 5c.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

There are significant typo mistakes and problems with english redaction, I must recommend a full grammatical review previous to do other corrections.

Lines 116-119, the certificate can be referred instead of declare the chemical composition, then a treacebilty can be more useful.

The anova results are weak, there are no evidence that the analyzed variables has a significant impact upon the response. Also, r^2, r^2(adj.) and r^2(pred.) should be reported to validate the precision of the statistical methods. Authors, should explain how this model can be useful to optimize results when there are higher p-values than 0.05 that suggests a non relevant impact upon the response.

• What specific improvements should the authors consider regarding the methodology?

As I previously mentioned, there are some important issues that authors should review before going further. In that sense, authors should explain and declare the all correlation values (Rˆ2) that minitab yields in order to validate mathematical model. It is worth mentioning, although graphs show evidence of influence of variables upon the response, however this can be misleading since the software adjusts scales automatically. Also, P-values are too high to reveal a great impact upon the responses, authors should explain more deeply the statistical analysis and make some strong arguments that involve correlation, p-values, to mention few. Otherwise, the experimental procedures can be catalogued as incorrect or weak (variables not impact response).

Comments on the Quality of English Language

There are significant typo mistakes and problems with english redaction, I must recommend a full grammatical review previous to do other corrections.

Author Response

R4.

Open Review

Comments and Suggestions for Authors

There are significant typo mistakes and problems with english redaction, I must recommend a full grammatical review previous to do other corrections.

1. We would like to thank the reviewer for the suggestions. The manuscript was grammatical review. Please refer to the revised manuscript.

Lines 116-119, the certificate can be referred instead of declare the chemical composition, then a treacebilty can be more useful.

404. The steel trademark is DX52D, with quality certificate is emitted by Bamesa SA, according to DIN 50049/ISO 404.

The anova results are weak, there are no evidence that the analyzed variables has a significant impact upon the response. Also, r^2, r^2(adj.) and r^2(pred.) should be reported to validate the precision of the statistical methods. Authors, should explain how this model can be useful to optimize results when there are higher p-values than 0.05 that suggests a non relevant impact upon the response.

R: We would like to thank the reviewer for the insightful feedback. The Anova method is very important for the results optimization, even when p-values are higher than 0.05, in order to capture some trends and relations useful for prediction, particularly for complex processes like projection welding in which the main process parameters often interact and affect outputs in a nonlinear way. The analysis helped in prioritizing the parameters for control and optimization, and for the sample selection in order to perform the microstructure analysis on the welded spots.

 

• What specific improvements should the authors consider regarding the methodology?

 

As I previously mentioned, there are some important issues that authors should review before going further. In that sense, authors should explain and declare the all correlation values (Rˆ2) that minitab yields in order to validate mathematical model. It is worth mentioning, although graphs show evidence of influence of variables upon the response, however this can be misleading since the software adjusts scales automatically. Also, P-values are too high to reveal a great impact upon the responses, authors should explain more deeply the statistical analysis and make some strong arguments that involve correlation, p-values, to mention few. Otherwise, the experimental procedures can be catalogued as incorrect or weak (variables not impact response).

Reply: We would like to thank the reviewer for the suggested improvements. As we’ve explained in a previous reply, the ANOVA analysis was conducted for prioritizing the parameters for control and optimization, and for the sample selection to perform the microstructure analysis on the welded spots. Even when p-values are higher, in the case of complex processes like projection welding, the analysis captured trends and relations useful for prediction.

 

Comments on the Quality of English Language

There are significant typo mistakes and problems with english redaction, I must recommend a full grammatical review previous to do other corrections.

R: We would like to thank the reviewer for the suggestions. The manuscript was grammatical review. Please refer to the revised manuscript.

 

Author Response File: Author Response.pdf

Reviewer 5 Report

Comments and Suggestions for Authors

In this work, thin aluminized steel sheets (low carbon) subjected to a multi-spot projection welding process were studied. The authors investigate the impact of welding parameters on the mechanical properties through the tensile strength and fracture mode tests. The research work is of interest to the scientific community, especially because of the technological applications in the industry; their research work is relevant and has been supported by statistical analysis. Good manuscript, but in its body, several syntax and grammatical errors must be corrected. The manuscript could be accepted for publication in this Journal after minor corrections.

 

Some particular comments

The authors must write a more comprehensive abstract with a clear-cut idea of their research work and output in a quantitative form. The authors should include the best findings of the work. The current abstract is merely descriptive.

 

The authors claim: “Cross-sections were prepared through the welded points to examine the microstructure of the welded area and to measure the microhardness in the weld and the heat affected zone”; however, in the manuscript, three is no results of microhardness. Could the authors clarify it?

 

On page 10, the authors claim: ” In the aluminized layer, interdendritic cracks have been developed in sample III/2 (for the welding power of 19 kVA)”. To support their result, the authors should include an optical microscopic image to identify the dendrite microstructure. Also, the authors affirm that the cracks obey the rapid heating; however, other samples also undergo the same heating treatment, and the cracks do not occur. The authors could clarify and improve the discussion in this way.

 

The authors claim: “The chemical composition variation on either side of the welded interface is due to mutual diffusion of elements during the welding process. However, to clarify it, the authors must provide a line scan EDS analysis and show an elemental concentration profile along the line between the substrate and welding. It will permit us to know the change in the concentration of each element along the interface boundary.

 

 

 

Author Response

R5.

Open Review

Comments and Suggestions for Authors

In this work, thin aluminized steel sheets (low carbon) subjected to a multi-spot projection welding process were studied. The authors investigate the impact of welding parameters on the mechanical properties through the tensile strength and fracture mode tests. The research work is of interest to the scientific community, especially because of the technological applications in the industry; their research work is relevant and has been supported by statistical analysis. Good manuscript, but in its body, several syntax and grammatical errors must be corrected. The manuscript could be accepted for publication in this Journal after minor corrections.

 

Some particular comments

The authors must write a more comprehensive abstract with a clear-cut idea of their research work and output in a quantitative form. The authors should include the best findings of the work. The current abstract is merely descriptive.

1. Thank you for this valuable suggestion. We’ve modified the summary.

The authors claim: “Cross-sections were prepared through the welded points to examine the microstructure of the welded area and to measure the microhardness in the weld and the heat affected zone”; however, in the manuscript, three is no results of microhardness. Could the authors clarify it?

1. Thank you for this valuable suggestion. We’ve added results for microhardness.

On page 10, the authors claim: ” In the aluminized layer, interdendritic cracks have been developed in sample III/2 (for the welding power of 19 kVA)”. To support their result, the authors should include an optical microscopic image to identify the dendrite microstructure. Also, the authors affirm that the cracks obey the rapid heating; however, other samples also undergo the same heating treatment, and the cracks do not occur. The authors could clarify and improve the discussion in this way.

1. We ‘ve changed the picture with a clearer one.

The authors claim: “The chemical composition variation on either side of the welded interface is due to mutual diffusion of elements during the welding process. However, to clarify it, the authors must provide a line scan EDS analysis and show an elemental concentration profile along the line between the substrate and welding. It will permit us to know the change in the concentration of each element along the interface boundary.

1. We’ve added the image with a graph of the elements profile through the interface between the coating and the substrate (Figure 6).

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

All of my concerns have been well addressed, and now it can be accepted.

Author Response

Thank you very much for review!

Reviewer 2 Report

Comments and Suggestions for Authors

As a follow up to the previous comments of the reviewer, the manuscript is significantly improved. However, the concerns of the reviewer are: 

1. The impact of the work is still questionable.
2. In the conclusions section, authors need to correlate the microstructural evolution in the welds with the breaking force. 

Comments on the Quality of English Language

English language quality needs significant improvement.

Author Response

Comments and Suggestions for Authors

1. The impact of the work is still questionable.

1. Thank you for this comment. We added this sentence in Introduction.

Continuous improvements in the aluminizing process have expanded the possible applications of steel components coated with thin layers of Al or Al-Si alloys. Such semi-finished products are often found in the manufacture of components for the automotive industry or in the production of baking molds for the food industry. Since many aluminized steel components are welded, it is important to know the phenomena occurring in the molten core area, which affects the strength characteristics of the joints. Currently, few references in specialized literature have addressed this issue.

2. In the conclusions section, authors need to correlate the microstructural evolution in the welds with the breaking force. 

 

1. Thank you for valuable comment. The following sentence has been added to Conclusion.

The welded area microstructure analysis highlighted that a good correlation between the values ​​of current, time and welding pressure is compulsory. Thus, if the pressure is too low, the brittle compounds that form because of the reactions between the surface layer (Al-Si alloy) and iron are localized on the midline of the joint and substantially reduce the tensile strength. For the analyzed cases, increasing the pressure from 2.8 to 5 bar allowed reducing the current values to obtain a good joint strength from 20.5 to 17.7kVA. Increasing pressure allows the brittle compounds to be ejected into the periphery of the weld area, increasing their strength.

Reviewer 4 Report

Comments and Suggestions for Authors

None

Author Response

Thank you for taking the time to review our work.