| Summary: | In this work, we studied the effects of different reinforcements on a metal matrix composite (MMC) using molecular dynamics (MD) simulations, where graphene was chosen as the two-dimensional (2D) material and diamond was selected as the three-dimensional (3D) material. Sintering and tensile processes were conducted on the MMC models containing reinforcements of various sizes, and the effects of reinforcements with the same surface area were compared. The results indicated that the 2D material was more beneficial for sintering at the heating stage, producing a higher-density structure. The volume of Al atoms fell from 752 to 736 nm<sup>3</sup> as the graphene size in the composite system increased. However, a slight increase from 749 to 755 nm<sup>3</sup> was observed when the diamond radius was small. Converted to relevant metrics in the experiments, the density of the composite reached 2.84 g/cc with a 3.3 wt.% addition of single-layer graphene (SLG) and 2.87 g/cc with a 15.4 wt.% addition of diamond, and the results were slightly higher than the experimental reports. Both SLG and diamond could reduce the number of arranged Al atoms from 43,550 to approximately 35,000, and bilayer graphene (BLG) with the largest size could further decrease the number of arranged atoms to nearly 30,000, implying that grain refinement could be obtained by increasing the surface area of reinforcements. Considering the scale of these models, the reinforcement size and pore location in the initial structures were deemed to have an impact on the mechanical properties. The composite with the largest proportion of SLG showed an increase of more than 1.6 GPa in tensile strength; however, BLG showed a significant drop of 1.9 GPa when stretched in the normal direction, as the large interlayer space acted as a large hole in tension. The diamond size did not appear to affect the strengthening effects. Nevertheless, the elongation values of composites with graphene were generally 35% higher than the Al-diamond composites.
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