Influence of secondary phases in A356 MMCs on their mechanical properties at macro- and nanoscale

Metal matrix composites are very inhomogeneous materials, and their properties depend on various parameters (production process, constituents, their interfaces, etc.). The influence of SiC microparticles (40 μm) reinforcement and graphite macroparticles (200–800 μm) addition on the mechanical properties of Al–Si A356 alloy, produced by compocasting, has been assessed using macro- and nanoscale measurements of hardness and modulus of elasticity. The Al makes over 90 wt% of the A356 alloy, so the nanoscale measurements were performed on different α phase regions on each material (core of α phase, eutectic α phase, and α phase near the phase boundaries α phase/secondary phases). The results showed that there is no direct correlation between mechanical properties on macro- and nanoscale. The nanoscale results also showed that the secondary phases (SiC and graphite particles) can have significant effect on the mechanical properties on the atomic level, i.e. in the α phase regions very close to the secondary phases.