**4. Conclusions**

Al–Cu composite materials were successfully prepared using mechanical ball milling and SPS. The Cu powder was dispersed in Al powder through the ball milling process, and the obtained composite powders were analysed using SEM. It was determined that the ball milling process was suitable for preparing composite powders. ICs were created from reactions between the Al and Cu during SPS, and their presence in the composites was confirmed by the XRD and EDS analysis results. Regardless of the composition, the Al–Cu composite materials exhibited higher Vickers hardness values than pure Al and Cu. The Al–50Cu composite exhibited the highest Vickers hardness of approximately 151 HV. The observed strengthening e ffects are considered to be related to the formation of intermetallic compounds, which were formed from the reaction between Al and Cu via micro-plasma sparks during the SPS process and detected in the X-ray di ffraction and EDS analyses. The Al–50Cu composite with a higher content of intermetallic compounds exhibited lower thermal conductivity. It is suggested that the properties of the Al–Cu composites were a ffected by the presence of the ICs. Nevertheless, SPS can be considered an e ffective process for fabricating Al–Cu composite materials.

**Author Contributions:** Conceptualization, K.K. and H.K.; Methodology, K.K.; Validation, K.K. and D.K.; Formal analysis, K.K.; Investigation, K.K., K.P., D.K., M.C. and S.C.; Writing—original draft preparation, K.K.; Writing—review and editing, K.K. and H.K.; Visualization, K.K., D.K. and M.C.; Supervision, H.K.; Project administration, H.K.; Funding acquisition, H.K.

**Funding:** This research was funded by the Commercializations Promotion Agency for R&D Outcomes (COMPA-2019K000076) funded by the Ministry of Science and ICT (MSIT).

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