Effect of GNPs on Microstructure and Mechanical Properties of Hot-Press Sintered GNPs/Mg-8Al-1Sm Composites

Achieving a balance between strength and toughness is crucial for developing high-performance magnesium-based composites. In this study, a novel GNP/Mg-8Al-1Sm composite was successfully prepared via hot-press sinter with varying weight fractions of graphene nanoplatelets (GNPs) (0, 0.4, 0.7, and 1.0 wt.%). The results reveal that as the GNP content increases, the Mg₁₇Al₁₂ precipitates undergo more phase transitions, while no reaction products are formed at the GNP/Mg-8Al-1Sm matrix interface. The interface of the composite was characterized via transmission electron microscopy (TEM), and it was found that the interface bonding was favorable with uniform dispersion of GNPs in the 0.4 wt.% GNPs/Mg-8Al-1Sm composite, which contributed to the enhanced mechanical properties of the material. The mechanical performance of the composites initially improves with increasing GNP content, reaching a maximum at 0.4 wt.% GNPs. At this composition, the ultimate compressive strength, yield strength, and fracture strain increase by 28.8, 56.5, and 10.4%, respectively, compared to the pure Mg-8Al-1Sm matrix, with values of 335, 200.8 MPa, and 10.6%. Further analysis of the strengthening mechanisms revealed that thermal mismatch strengthening, fine grain strengthening, dispersion strengthening, and GNPs carrying capacity collectively contribute to the enhanced mechanical properties. Specifically, thermal mismatch strengthening accounted for the largest portion of the total strengthening effect, highlighting its primary role in reinforcing the composite. Graphene can also hinder crack propagation and improve toughness by crack bridging, deflection, and pulling. These findings demonstrate the potential of GNPs as effective reinforcements for improving the strength and toughness of magnesium-based composites.