**4. Conclusions**

In this paper, a high-speed photography system and image processing technology were used to extract the characteristics of arc profile, the droplet transfer and the weld pool oscillation. The influence of DP-GMAW welding parameters on heat input, pressure acting on weld pool, weld pool size and oscillation amplitude have been calculated. Additionally, the internal relation between weld pool behavior and microstructure was analyzed. The conclusions are as follows:


**Author Contributions:** Methodology, T.C.; software, T.C.; investigation, T.C., P.Z. (Peng Zhang), writing—original draft preparation, T.C., P.Z. (Peng Zhang); writing—review and editing, S.X., T.C., B.W., P.Z. (Peizhuo Zhai); supervision, S.X.; project administration, S.X., W.L.; funding acquisition, S.X. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was funded by the National Natural Science Foundation of China, grant No.51675269 and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

**Acknowledgments:** The authors gratefully acknowledge the financial supports by the National Science Foundation of China under Grant numbers 51675269, as well as the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

**Conflicts of Interest:** The authors declare no conflict of interest.
