**6. Patents**

Cao, B.; Yang, K.; Huang Z. Adaptive control method and system for plasma electrolytic oxidation process. *China ZL* 201410036861.5, 2016.

**Author Contributions:** Conceptualization and Methodology, K.Y. and B.C.; Investigation, K.Y., H.H., J.C. and B.C.; Resources, K.Y., H.H. and B.C.; Writing—original draft, K.Y. and J.Z.; Writing—review & editing, J.Z., H.H. and B.C.; Funding acquisition, H.H., and J.C.

**Funding:** This research was funded by National Natural Science Foundation of China (grant number 51865004) and Foundation of Guizhou Educational Committee (KY [2017]106).

**Acknowledgments:** The authors are grateful for technical support and equipment provided by Guangzhou Jing Yuan Electrical Equipment Limited Company.

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