Effect of carbon nanotubes and high temperature extrusion on the microstructure evolution of Al-Cu alloy

CNTs/Al composites were prepared using flake powder metallurgy. The effects of CNTs and high temperature extrusion on mechanical properties and density of the material were investigated through analyzing crystal size, distribution and the change (size, chemistry and crystal structure) of precipitates and CNTs. Results show that hardness and density of the composites can be increased via extrusion and CNTs addition. Moreover, extrusion leads to refined precipitates with uniform distribution and partial dissolution compared to the as-sintered. The grains become smaller after addition of CNTs. Four types of phases distributed homogeneously in CNTs/Al composites: CNTs, Al2Cu, Al2O3 and nano-sized Al4C3. The intermetallic compound Al4C3 as interlayer is beneficial to strengthen adhesion between CNTs reinforcement and the Al matrix. The uniformly distributed dispersions of CNTs, Al2Cu, Al2O3 and Al4C3 can refine the crystalline structure, thus improving mechanical performance. Combined strengthening mechanisms are identified in the composites, containing grain boundary strengthening, dispersion strengthening and better load transfer from the Al-Cu matrix to CNTs though Al4C3.