Anisotropic thermal conductivity of aluminum matrix composites reinforced by graphene nanoplates and ZrB₂ nanoparticles

This study investigates the anisotropic thermal conductivity of aluminum matrix composites reinforced with graphene nanoplates (GNPs) and in situ ZrB₂ nanoparticles, while simultaneously maintaining high strength and toughness. A discontinuous layered GNPs-ZrB₂/AA6111 composite was prepared using in situ melt reactions and semi-solid stirring casting technology, combined with hot rolling deformation processing. Microstructural analysis revealed that the GNPs were aligned parallel to the rolling direction–transverse direction (RD–TD) plane, whereas the ZrB₂ nanoparticles aggregated into cluster strips, collectively forming a discontinuous layered structure. This multilayer arrangement maximized the in-plane thermal conductivity of the GNPs. The tightly bonded GNP/Al interfaces with the locking of CuAl₂ nanoparticles ensured that the GNP fully exploited their high thermal conductivity. Therefore, the GNPs-ZrB₂/AA6111 composite achieved high in-plane thermal conductivity (230 W/(m·K)), which is higher than that of the matrix (206 W/(m·K)). The improved in-plane thermal conductivity is primarily attributed to the exceptionally high intrinsic in-plane thermal conductivity of the GNPs and their two-dimensional layered structure. However, the composite exhibited pronounced thermal conductivity anisotropy in the in-plane and through-plane directions. The reduced through-plane thermal conductivity is predominantly caused by the intrinsically low through-plane thermal conductivity of the GNPs and the increased interfacial thermal resistance from the additional grain boundaries.