## 3 Results and Discussion
### Compression Properties  
The compression test provided vital properties such as yield stress (\(\sigma_{\rm y}\)), compressive strength (\(\sigma_{\rm{uc}}\)), and fracture strain (\(\varepsilon_{\rm{f}}\)). The compressive properties of the Al-4 Cu/(Al\({}_{2}\)O\({}_{3}\))\({}_{\rm x}\) AMCs processed under the different studied conditions were measured. It was revealed that increasing the compaction pressure and Al\({}_{2}\)O\({}_{3}\)wt.% resulted in significant increases in the \(\sigma_{\rm y}\) and \(\sigma_{\rm{uc}}\) of the compacted discs. Moreover, decreasing the H/D value caused an increase in the compressive properties and decreased the \(\varepsilon_{\rm{f}}\).  
As tabulated in Table 11 (Appendix A), the \(\sigma_{\rm y}\) and \(\sigma_{\rm{uc}}\) of the Al-4 Cu sintered discs compacted under a pressure of 500 MPa for H/D\(=1.5\) were 183 MPa and 224 MPa, respectively. To investigate the effect of the compaction pressure, it was revealed that increasing the compaction pressure to 600 MPa using the H/D\(=1.5\) resulted in 2.73% and 7.6% increases in the \(\sigma_{\rm y}\) and \(\sigma_{\rm{uc}}\), respectively. For a compaction pressure of 600 MPa, the reduction in the H/D to 1 resulted in additional increases in the \(\sigma_{\rm y}\) and \(\sigma_{\rm{uc}}\) of 4.8% and 9.1%, whereas an H/D of 0.75 resulted in increases in the \(\sigma_{\rm y}\) and \(\sigma_{\rm{uc}}\) of 4% and 6.1%, respectively, compared to the discs compacted at 500 MPa. Moreover, increasing the compaction pressure up to 900 using an H/D = 1.5 resulted in significant increases in both the \(\sigma_{\rm y}\) and \(\sigma_{\rm{uc}}\) of 6% and 11.2%, respectively. For the counterparts compacted using an H/D of 1.25, increases in the \(\sigma_{\rm y}\) and \(\sigma_{\rm{uc}}\) of 7% and 14.7%, respectively, were recorded. Furthermore, the H/D of 1 led to increases in the \(\sigma_{\rm y}\) and \(\sigma_{\rm{uc}}\) of 4.5% and 14.4%, respectively, compared to the discs compacted at 500 MPa.  
Furthermore, increasing the Al\({}_{2}\)O\({}_{3}\) content to 2.5 wt.% resulted in 2.27% and 4.03% increases in the \(\sigma_{\rm y}\) and \(\sigma_{\rm{uc}}\) for sintered discs with an H/D = 1 compacted under 500 MPa, respectively. Additional Al\({}_{2}\)O\({}_{3}\) strength, with 5, 7.5, and 10 wt.%, resulted in \(\sigma_{\rm y}\) increases of 1.95, 0.95, and 2.37, respectively, and \(\sigma_{\rm{uc}}\) increases of 5.1%, 1.41%, and 1.63%, respectively, compared to the Al-4 Cu discs compacted at 500 MPa. In addition, increasing the compaction pressure up to 900 MPa increased the \(\sigma_{\rm y}\) and \(\sigma_{\rm{uc}}\) compared to the discs compacted under 600 MPa. As the Al-4 Cu/(Al\({}_{2}\)O\({}_{3}\))\({}_{2.5}\) recorded increases of 23.67% and 21.7%, Al-4 Cu/(Al\({}_{2}\)O\({}_{3}\))\({}_{5}\) had increases of 32.37 and 37.21%, Al-4 Cu/(Al\({}_{2}\)O\({}_{3}\))\({}_{7.5}\) had increases of 42.5 and 42.64%, and Al-4 Cu/(Al\({}_{2}\)O\({}_{3}\))\({}_{10}\) had increases of 45.19 and 34.53% in the \(\sigma_{\rm y}\) and \(\sigma_{\rm{uc}}\), respectively. Additionally, the \(\varepsilon_{\rm{f}}\) decreased with decreases in the H/D and increases in both the compacted pressure and the Al\({}_{2}\)O\({}_{3}\) content. Increasing the Al\({}_{2}\)O\({}_{3}\) wt.% up to 10 resulted in decreases in the \(\varepsilon_{\rm{f}}\) of the sintered discs compacted under 900 MPa of 22% for an H/D = 1.5 and of 36% for an H/D = 1, compared to 2.5 wt.% Al\({}_{2}\)O\({}_{3}\). An increase in the strength and a decrease in the \(\varepsilon_{\rm{f}}\) with increases in the wt.% of Al\({}_{2}\)O\({}_{3}\) and the compaction pressure can be attributed to the grain refinement and the brittle nature of Al\({}_{2}\)O\({}_{3}\).