Magnetic Characterization of the Nugget Microstructure at Resistance Spot Welding

Round 1

Reviewer 1 Report

The paper proposed a method to measure and evaluate the magnetic properties of these regions, especially of the base material and the weld. The paper also showed different measuring methods and approaches. The reviewer has the following comments before it can be published.

1. How is the influence for Epstein frame? additional expense is the reason?

2. MAT4 shows the lowest coercivity Hc followed by MAT2 and MAT1 in Fig. 8. Could the author give more explanation?

3. Fig. 15(a), why I = 0 A, the magnetic flux density can also be recognized here?

4. In the future simulation, magnetic field module in COMSOL is recommanded.

Author Response

Thank you for your review, questions and advice, which we answer as follows: 

1. How is the influence for Epstein frame? additional expense is the reason?
   
   The additional expense is not the main reason, as can be seen from the further course of the sentence. The main reason is, that there was no success from the beginning to measure the pure weld structure with an Epstein-frame. So in combination with the main reason and the additional expense, the experiments were discarded.
   
   
2. MAT4 shows the lowest coercivity Hc followed by MAT2 and MAT1 in Fig. 8. Could the author give more explanation?
   
   The authors added a more detailed explanation in the text:
   The reason for the different coercivity levels can be found in the microstructure on the one hand and in the alloying elements on the other. MAT1 is a quenched and tempered material with a martensitic microstructure, while MAT2 and MAT4 have a ferritic microstructure. Martensitic microstructures usually exhibit higher coercivity than ferritic microstructures, as also reported in~\cite{Hunicke.2003}. The differences in the MAT2 and MAT4 ferritic materials can be attributed to the alloying elements. MAT2 contains aluminum and titanium, while in MAT4 these elements are not alloyed. Both elements lead to higher coercivity. In addition, the alloying elements lead to a finer microstructure with smaller grain sizes, which also results in higher coercivity~\cite{Kneller.1962}.
   
   
3. Fig. 15(a), why I = 0 A, the magnetic flux density can also be recognized here?
   
   The measured magnetic flux density is smaller than 100µT for all samples at 0A. The demagnetization process might be the reason, since it is done manually by moving the samples across a sinus-demagnetizer.
   
   
4. In the future simulation, magnetic field module in COMSOL is recommanded.
   
   This is a good advice. Thank you. Right now, we are using ANSYS. Do you have experience with COMSOL?

Reviewer 2 Report

This paper presents methods to measure and evaluate the magnetic properties of the joint quality of resistance spot welding. Based on the hypothesis that the test results of the passive magnetic flux density testing are influenced by the microstructure of the nugget of a spot welded joint, various measurement methods were investigated to characterize the magnetic behavior of the microstructures of the weld and the base material. The analysis presents a valuable reference for measure and evaluate the the joint quality of resistance spot welding.

Author Response

Thank you for your review.