## 3 Results and Discussion
Since it has been reported in the microstructure that the addition of graphene nanoparticles was attributed to grain refinement, the evidence was concluded by XRD result data. As the graphene nanoparticles served as the nucleation substrate for the \(\alpha\)-Mg phase to provide a  
Figure 3: Surface characterization of AZ31/1.75 wt.%GNP prepared at different compaction pressures, sintering temperatures, and sintering times. The annotation for the symbol used in the microstructures from S1 to S9 is depicted in Table 5.  
reduction in the grain growth. Therefore, most peak (\(\alpha\)-Mg phase) depictions were acting as a nucleation site for grain reduction. Other than that, the microstructure formed inferred that GNP was distributed along the \(\alpha\)-Mg phase that was accompanied by the presence of MgO oxide. The addition of graphene nanoparticles in the AZ31 matrix composite enhances grain refinement compared to the base alloy AZ31. Figure 4b shows the variation in grain refinement with compaction pressure, sintering temperature, and sintering time. The result indicated that the effective densification of reinforcement in the matrix reduces the grain size more effectively imparting the proper bonding between the matrix and reinforcement. The proper infusion of reinforcement in the matrix further reduces the porosity (%) of the composite as shown in Figure 4c. Therefore, the reduction in grain size and porosity (%) ultimately enhances the mechanical properties of the composite compared to the base alloy. The compressive strength of the composite was depicted to be increased with the addition of graphene nanoparticles compared to the base alloy (AZ31). It is due to the effective transfer of loads from the matrix to graphene nanoparticles that occurred owing to the good wettability of graphene nanoparticles in the magnesium matrix. Thus, a good  
Figure 4: The characterization of the synthesized samples: (**a**) X-ray diffraction (XRD) patterns of samples S1–S9, highlighting the presence of the \(\alpha\)-Mg phase and MgO phase. The diffraction peaks confirm the phase composition of the developed materials, with consistent peak intensities across different samples. (**b**) Grain refinement of the samples compared to AZ31, demonstrating a progressive reduction in grain size from S1 to S9. The decreasing trend in grain size indicates effective grain refinement through the applied processing parameters. (**c**) The porosity percentage of the synthesized samples, showing a gradual reduction in porosity from S1 to S9. The lower porosity in later samples suggests improved densification and material integrity, which can positively influence mechanical properties. mechanical bonding was revealed between the reinforcement and matrix. The mechanical bonding between the reinforcement and the matrix was enhanced during the sintering process, allowing the effective diffusion of reinforcing material occurring in the matrix and enabling the improvement in the compressive strength of the composite. Figure 5a shows the compressive strength for all the samples prepared at different process parameters. The compressive strength of the composite is obtained to be higher for the S9 sample than the base AZ31 alloy (358 MPa). The effective infusion of nanoparticles in the composite at the optimized parameter signifies the proper diffusion between reinforcement in the AZ31 alloy. Therefore, the bonding strength between the reinforcement and matrix material increased which resulted in better compressive strength. The microhardness of the composite was also observed to be increased with the addition of graphene nanoparticles and obtained to be higher for the S9 sample (108.5 HV) as shown in Figure 5b. The proper diffusion of reinforcement resists localized deformation in the matrix during the indentation. Thus, a high value of microhardness was observed for the S9 sample compared to other samples and the base alloy.