Preparation And Study Of CNTs / Al2024 Composites

CNTs/Al composite materials, with light weight, high specific strength and good high temperature performance is expected to be used in automobile, aerospace, electronics and other fields. It will become a hotspot of research of new materials. CNTs owning one-dimensional nanomaterials, excellent mechanical and eletrochemi-cal properties, can improve the mechanical properties of composite materials, when Carbon nanotubes were dispersed in the aluminum substrate.At present, the method of preparation of CNTs/A12024 composite powder have the mechanical ball grinding,gas phase deposition and so on.Whereas, the mechanical ball grinding can effectively disperses CNTs uniform into aluminum substrate. The method of peparation of CNTs/A12024 composites have methods of casting, powder metallurgy method, and so on. In this paper, CNTs/A12024 composites was prepared by powder metallurgy method.At first, the structure of purified carbon nanotubes, functional group content and impurity content of carbon nanotubes are studied in purification process. The results showed that CNTs attached a large number of functional groups, opened fracture part, Carbon layer structure integrity and removed impurities, using VHNO3:VH2SO4=3:1 conducted CNTs.Then, using the mechanical ball milling method prepared CNTs/A12024 composite powder. Single factor method was used to study parameters of ball milling. Using response surface method optimize process parameters for in High-energy Ball Milling preparation of CNTs/A12024 Composites. The research results show that the optimal parameters were 1.5h milling time,800/1000rpm rotational speed, mass fraction of CNTs 2.5%, Ball to powder ratio 25:1 and mass fraction of process control agent 0.5%.The maximum UST and hardness of CNTs/A12024 composite materials are 267.25MPa and 256.8HV. What’s more, CNTs can dispersed homogeneously in the A12024 substrate and CNTs have played an important role in blocking reunion powder and refine grain.The effect of the cold press sintering, cold rolled annealed and re-pressure re-burn processes on the mechanical of composite material were studied and tested in room temperature. The optimum conditions of sintering molding were the first pressure 20MPa, the sintering temperature 900℃,the heat preservation time 60min, the re-pressure 30MPa, the sintering temperature 300℃, the heat preservation time 30min and the pressure holding 10min. The maximum UST and hardness of CNTs/ A12024 composite materials are 291MPa and 258HV, respectively.They relative matrix increased by 94% and 43%, respectively. Through TEM observation, defect of carbon nanotubes reaction with aluminum matrix generated A14C3 phase. So interfacial bond strength between CNTs and A12024 matrix was good, resulting in the cracks spreading across the aluminum powder rather than the between CNTs and A12024 matrix interface. As a result, much dimples and ridges are formed in this composite,proving that CNTs play a role in bridging and strengthening the matrix alloy.