**4. Conclusions**

It was shown that the CsF-RbF-AlF3 flux doped with GaF3 obtained the maximum spreading area, both on 6061 aluminum alloy and Q235 low-carbon steel, and reached the highest shear strength of 126MPa. The above analysis led to the following conclusions:


**Author Contributions:** Conceptualization, S.X.; methodology, J.Z.; software, Z.Y.; validation, Z.Y.; formal analysis, Z.Y.; investigation, Z.Y.; resources, S.X.; data curation, Z.Y.; writing—original draft preparation, Z.Y.; writing—review and editing, Z.Y.; visualization, Z.Y.; supervision, S.X.; project administration, S.X.; 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. 51375233 and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

**Acknowledgments:** We gratefully acknowledge the support of Jiangsu Higher Education Institutions for providing a scholarship for Zhen Yao. Songbai Xue acknowledges financial support from the National Natural Science Foundation of China, Grant No. 51375233.

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