Microstructures and mechanical properties of nano-C and in situ Al2O3 reinforced aluminium matrix composites processed by equal-channel angular pressing

In this study, the powder metallurgy method was used to prepare nano-C and in situ Al2O3 hybrid reinforced Al matrix composites, the grain size was refined, and the dispersion of reinforcements was improved by equal-channel angular pressing (ECAP). Twin Si and slip steps were present in the composites reinforced by 0.75% carbon nanotubes (CNTs), 0.25% graphene nanoplatelets (GNPs), and Al2O3 by three ECAP passes. The interface between the CNTs and the matrix was closely bonded. The γ-Al2O3 particles and fibres were generated by an in situ method, and the nucleation and interfacial orientation of Al2O3 were discussed. With the increase in ECAP passes, the electrical and mechanical properties of the composites were improved. The electrical resistivity of the composites reinforced with 0.5% GNPs after three ECAP passes showed the lowest value of 3.64 × 10−8 Ωm. The maximum hardness of the composites reinforced with 1.0% CNTs after three ECAP passes was 321.9 HV. The compressive strengths of the composites improved. The strengthening mechanism of the ECAP-treated Al matrix composites was summarised as dislocation strengthening, dispersion strengthening, grain boundary strengthening, and load transfer