## 4 Conclusions  
This study fabricated a sound SiC/AA2024 metal matrix composite using stir-casting (SC) and die-casting (DC) processes. Effects of the DC process were confirmed to allow comparison of the effects of the two process types on the Al composites, and the microstructures and mechanical properties of specimens of various volume fractions were evaluated.  
1. Microstructural observation showed particle clusters and pores in the aluminum matrix composites (AMCs) after the SC process. After the DC process, agglomerations and pores were removed and the particle distribution was more uniform than in the case of AMCs formed by the SC process. This is attributed to two-stage melt injection during the DC process prevented air inflow and induced rapid solidification, which led to grain refinement and uniform particle dispersion.
2. The grain size of the DC-processed composite was 17.67 \(\upmu\)m, which is approximately a 75% decrease compared to the composite fabricated by the SC process (68.06 \(\upmu\)m). This result shows that the grain refinement might contribute to strengthening the composite. Moreover, with the DC process, the degree of dispersion of SiC particles increased. The distribution of the reinforcement was quantitatively analyzed, and the results showed decreased dispersion index (DI) values for die-cast samples, which indicates the effectiveness of the DC process in improving the reinforcement dispersion.
3. The deviation of the hardness value decreased after the DC process. Especially, the maximum hardness value was 57.6 HRB at 9 vol.% SiC; this is an approximately 30% higher value than that of the matrix. Moreover, the hardness of the DC composite improved by about 32% compared to that of the AMCs fabricated by the SC process at the same volume fraction.
4. In the case of specimens fabricated by the SC process, the tensile strength decreased as the volume fraction of SiC particles increased. On the other hand, specimens manufactured by the DC process tended to show increased tensile strength and elongation as the volume fraction increased. The maximum tensile strength was 313.7 MPa for the DC process, which is about two times higher than that of the composite produced by the SC process; the elongation increased by about four times.  
Figure 8: The stress–strain curves of the AMCs with different process.  
These results are attributed to the uniformly dispersed particles, which caused the load to transfer efficiently from matrix to reinforcement as well as to the strengthening effect of grain refinement in the DC process.  
Conceptualization, S.-K.L. and I.J.; methodology, S.C.; software, B.P.; validation, S.-B.L.; formal analysis, H.P.; investigation, S.S.; data curation, Y.K.; writing--original draft preparation, S.S.; writing--review and editing, I.J.; visualization, B.P.; supervision, I.J.; project administration, S.C.; funding acquisition, S.C. All authors have read and agreed to the published version of the manuscript.  
This research was financially supported by the Fundamental Research Program (PNK7380) of the Korea Institute of Materials Science.  
Not applicable.  
The data and analysis in this study are available on request from the corresponding author.  
This research was supported by the Basic Science Research Capacity Enhancement Project through a Korea Basic Science Institute (Core-facility for Converging Materials) grant funded by the Ministry of Education (2019R1A6C1010045).  
The authors declare no conflict of interest.