**4. Conclusions**

In this study, trace amounts of GaF3 and Ga2O3 nanoparticles were respectively added into CsF-AlF3 flux for brazing aluminum to carbon steels. The effects of these two nanoparticles on the flux activity and the spreadability of Zn-15Al filler metal on the base metal were comparatively investigated. The major conclusions were as follows:


**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 research 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.
