**5. Conclusions**

The welding qualitiesand tensile mechanical properties related to the metallurgical bonded microstructural characteristicsof FSW Al–Cu dissimilar joints are identified and discussed in this study. In addition, the relationship between welding quality and tensile strength, as well as the joint reliability, is investigated by the Weibull statistical analysis. The conclusions are drawn based on the above results and discussions:


**Author Contributions:** This study presented here was carried out in collaboration between all authors. C.-W.Y. conceived and designed the experiments; S.-J.J. performed the experiments; C.-W.Y. analyzed the data and wrote the manuscript. All authors reviewed the manuscript, and the authors hope that this manuscript can make its due contribution to the successful application of the high-performance FSW Al-Cu dissimilar joints.

**Funding:** The Ministry of Science and Technology (MOST) is the government agency dedicated to scientific and technological development. Its three main missions are promoting nationwide science & technology development, supporting academic research, and developing science parks.

**Acknowledgments:** This study was financially supported by the Ministry of Science and Technology, Taiwan (Contract No. MOST 107-2221-E-150-005) for which we are grateful.

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