A novel strengthening effect of in-situ nano Al2O3w on CNTs reinforced aluminum matrix nanocomposites and the matched strengthening mechanisms

Nano alumina whiskers (Al2O3w) were in-situ synthesized in carbon nanotubes (CNTs) reinforced aluminum matrix nanocomposites (AMNCs) which were fabricated by flake powder metallurgy (P/M). To study the strengthening effect of nano Al2O3w on CNTs reinforced AMNCs and clarify the strengthening mechanisms, the microstructures and mechanical properties of AMNCs are investigated. It is found that CNTs-Al2O3w reinforcements have a significant hybrid strengthening effect on tensile strength due to their uniform dispersion and good interfacial bonding with Al matrix. The strengthening mechanisms of CNTs-Al2O3w reinforcements are considered as a sum of load transfer, grain refinement, thermal mismatch and Orowan looping theory. The experimental strengths of AMNCs containing 0.25 and 0.5 vol% CNTs are well matched with the theoretical values calculated by the strengthening mechanisms. And the differences between them are less than 2.9%, which is highly effective for predicting the mechanical properties of CNTs-Al2O3w reinforced AMNCs. The predicted values indicate that load transfer mechanism from both CNTs and Al2O3w is dominant, improving UTS of 0.5CNTs reinforced flake AMNCs (228 MPa) by more than 79.5% in comparison with pure Al.