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It has been thoroughly investigated Al4C3 formed as a result of the reaction of graphene in the form of graphene nanoplates (GNPs) and aluminum from the metal matrix during annealing of an aluminum matrix composite with GNPs strengthener produced by powder metallurgical method. Carbide's microstructural and crystallographic characteristics have been determined using SEM, TEM, and HRTEM. The formation of Al4C3 depends on the annealing temperature and holding time. The carbides have rod-like shapes. They are distributed predominately at grain boundaries. The average length is 118 nm, and the average diameter is − 17 nm. The longitudinal orientation of carbides coincides with the extrusion direction and the tensile direction in most cases. The interfaces between the aluminum matrix and existing particles in the composite were estimated. The factors that lower the strength indicators of the composite are the following: i) the presence of an Al2O3 layer or shell between the carbide particles and the aluminum matrix because of the incoherent interface between the carbide and oxide; ii) the accumulation of carbide particles at grain boundaries and their unfavorable longitudinal orientation which leads to a lack of locking effect of the carbides and poor load transfer. Thus, the carbides brittle the boundaries and reduce the ductility; iii) the presence of even a tiny number of micro-sized carbides which increase the brittleness of the composite. [ABSTRACT FROM AUTHOR]

Aluminum-based composites containing 0.1-0.7 wt.% graphene were produced by the powder metallurgical process. The microstructure of the nanocomposites was studied using LM, SEM, EDS, TEM, and XRD. A relatively uniform distribution of graphene nano-platelets and compacted agglomerates in composites with different graphene contents was found. A mechanical bond between the nano-platelets and the aluminum matrix was established. Under the conditions used, neither particles nor nanoparticles of Al4C3 are formed. The microhardness and mechanical properties were studied. It was found out they are the highest in the composite containing 0.1% graphene. The change of these properties with the graphene content increasing has the same character. Agglomeration of GNPs occurs in all composites containing graphene, but a part of GNPs remain in a dispersed, non-agglomerated state. The microhardness and mechanical properties depend on this part of individual GNPs. It was proven that the observed increase in the yield strength of the studied composites is due to Orowan's strengthening mechanism. The fracture mechanism of GNPs de-bonding and pull-out from the aluminum matrix of the composite was experimentally proved. [ABSTRACT FROM AUTHOR]