Synthesis And Mechanical Properties Of In-situ CNTs Reinforced Al-Cu Alloy Matrix Composites

Carbon nanotubes(CNTs), owing to their nano-sized structure and superior physical, chemical and mechanical properties, have been regarded as one of the most promising reinforcement for metal matrix composites. However, since it is hard to achieve well dispersion, chemical stability and good interfacial bond between CNTs and metal matrix, the application of CNTs reinforced metal matrix composites is limited. On the other hand, CNTs reinforced Al alloy matrix composites have not aroused much attention, especially in the effect of CNTs on solution-aging process of heat treatable Al alloy. Based on the previous works of our group in CNTs/Al composites, in this study, in-situ synthesized CNTs reinforced Al-Cu alloy matrix composites were prepared, and the effect of CNTs on the heat treatment of Al-Cu alloy were discussed as well.Initially, CNTs were prepared on the surface of pure Al powder by in-situ synthesis, including impregnation, calcination and reduction, and chemical vapor deposition(CVD). Then a short-time ball milling was applied to achieve the homogeneous dispersion of CNTs in Al matrix. In addition, another process of impregnation and reduction was used to deposit nano-sized Cu particles on the surface of CNTs/Al composite powders. After another ball milling, Cu nanoparticles were well dispersed in the composite powders.CNTs/Al-Cu composite bulks were fabricated by powder metallurgy and the microstructure, hardness and mechanical properties of the composites were tested as well. SEM and XRD results show that well-dispersed Cu phases are converted to Al2 Cu phase so as to form the CNTs/Al-Cu composites during the procedure of sintering. CNTs have positive influences on the alloying process of Al-Cu alloy. After T6 heat treatment, the duration of peak aging has been shortened from 9h to 3h. In the tensile properties, the ultimate tensile strength of CNTs/Al-Cu composites has reached ~35.4% increase of Al-Cu, and a further increase has been achieved of ~20.4% after T6 heat treatment.The strengthening mechanism of CNTs/Al-Cu composites was discussed. The strengthening effect was controlled by two synergistic factors: the strengthening of CNTs and the effect of CNTs on the precipitation strengthening of Al-Cu alloy. As nano-sized reinforcement, CNTs has its own strengthening effect. In addition, the excellent interfacial bond between CNTs and matrix is in favor of further improvement of strength. Besides, CNTs can facilitate the process of heat treatment of Al-Cu alloy, decreasing the aging time and increasing the hardness and strength of peak aging.