Structure optimization for improving the strength and ductility of heterogeneous carbon nanotube/Al-Cu-Mg composites

Abstract Heterogeneous carbon nanotube (CNT)/Al-Cu-Mg composites, consisting of ductile zones (DZs) free of CNTs and brittle zones (BZs) rich of CNTs, were fabricated in powder metallurgy route. It was shown that the grain size and width of the DZs in the heterogeneous composites could be controlled by high energy ball milling (HEBM) on additional Al-Cu-Mg alloy powders. Appropriate grain refinement in the DZs and a medium DZ width were identified to be beneficial for improving the strength-ductility. Under the optimized condition, a heterogeneous CNT/Al-Cu-Mg composite exhibited 88% increase in the elongation and 2% increase in the tensile strength compared to the uniform composite. Although the yield strength of the heterogeneous composite was lower than that of the uniform composite, the appropriate grain refinement in the DZs was good for alleviating the low yield phenomenon. Furthermore, the abundant grain boundaries could reduce the local slip bands passing through the DZs, which could significantly relax the stress concentration of the BZs. As a result, the medium width DZs could contribute more to the plastic deformation, thereby further improving the strength-ductility. Finally, a model was proposed to assist the design of the heterogeneous structure parameters. The calculated optimized DZ size was in accordance with the DZ width of the heterogeneous composite with the best strength-ductility.