Fabrication of graphite-reinforced 6201Al matrix composite with simultaneous enhancement of mechanical and electrical properties by multi-pass friction stir processing

In this study, graphite-reinforced 6201 aluminum alloy matrix composites were fabricated by multi-pass friction stir processing. The mechanical properties and electrical conductivity of the composites were tested, the microstructure and composition of the composites were analyzed by scanning electron microscope and Raman spectroscopy. The results showed that the graphite-reinforced 6201Al matrix composite achieved simultaneous improvement of mechanical and electrical properties compared to the base material, with a 19.5 % increase in ultimate tensile strength and a 1.2 % increase in electrical conductivity. Microstructural and compositional analysis revealed that the graphite reinforcement in the composites was significantly fragmented during FSP, and its size decreased while the number of atomic layers reduced with increase in FSP passes. A directly bonded Al-C interface is observed between the graphite reinforcement and the matrix, and no interface products such as Al4C3 were generated. The graphite reinforcement in the matrix simultaneously serves as a hindrance to dislocation motion and the expansion of microvoids during the tensile process, thereby leading to an enhancement in the tensile strength of the composite. The improvement in the electrical conductivity of the composite is attributed to two factors. On one hand, the structure and properties of graphite-reinforced phase is transformed to be closer to graphene after the severe plastic deformation during FSP process. On the other hand, the directly bonded Al-C interface between the matrix and the reinforcement is able to transfer electrons across the interface.