Microstructure And Properties Of Carbon Nanotubes Reinforced 2024 Composites

This article mainly takes CNTs/2024 composite material as the research object.Firstly,it analyzes the immersion process of carbon nanotubes before and after coating with TiO₂ and the law of immersion of carbon tubes with different parameters into the melt from the perspective of thermodynamics,and then the composite material is heat treated to study the changes in the microstructure and mechanical properties of the composite material with different solution time and aging time.Finally,the corrosion mechanism of composite materials under different conditions is comparatively studied.The results show that the TiO₂ coating process used in this article is successful.After the coating treatment,the ceramic particles TiO₂basically cover the surface of the carbon tube,which reduces the intermolecular force between the carbon tubes and makes the carbon tubes easier to disperse.Under the same parameters（d=55nm,L=10μm）,compared with CNTs,CNTs@TiO₂ is easier to immerse into the melt spontaneously and has a larger spontaneous immersion angle range.The external energy required for the non-spontaneous immersion process in the later stage is greatly reduced by 52.9%.The same external energy is conducive to immersion of more CNTs@TiO₂ into the melt.When other factors are the same,carbon nanotubes with longer length and larger diameter are easier to immerse into the melt in the early stage,but the external energy required will be greater in the later stage.Therefore,the length and diameter of the carbon nanotubes should be considered comprehensively when considering the preparation of carbon nanotube-reinforced metal matrix composites by the fusion casting method.Furthermore,this article also investigated the influence of the addition of CNTs and the different solid solution time and different aging time on the microstructure and mechanical properties of the composite.With reference to previous studies,this paper sets the solid solution temperature as 495℃and the aging temperature as 180℃.The addition of 1.0 wt.%CNTs can refine the grains,the grain size is reduced from 124μm to 64μm,and the grain refinement effect reaches 48.4%,which is attributed to the effect of CNTs’Zener pinning grain boundaries.For 1.0 wt.%CNTs@TiO₂/2024 composite material,the better T6 heat treatment process is solution treatment（495℃,2h）+aging treatment（180℃,12h）.After T6 heat treatment,the Al₂Cu Mg phase and Al₂Cu phase are uniformly precipitated in the composite material,most of which are in a discrete state,and the edges of the precipitated strengthening phase are passivated compared to those before T6 heat treatment.From the as-cast state to the composite material and then to the subsequent T6 heat treatment,the hardness increased significantly,from96HV to 170HV,an increase of 77.1%.When 1.0 wt.%CNTs is added,the UTS,YS and E of the composite material reach 230MPa,145MPa and 3.8%,respectively,which are 33.7%,34.3%and-17.4%higher than the 2024 alloy matrix.After T6 heat treatment,the UTS and YS of the T6 composite material reached 324MPa and 219MPa,respectively,which were 40.9%and 42.1%higher than the composite material.Its elongation rate reaches 6.3%,which is an increase of 37.0%compared to 2024 alloy.The fracture of the three materials is a good proof of the improvement of mechanical properties.On the other hand,adding 1.0 wt.%CNTs will increase the pitting sensitivity of the 1.0 wt.%CNTs@TiO₂/2024 composite material and reduce the corrosion resistance.The results show that compared with 2024 alloy,the corrosion potential of T4composite material and T6 composite material increased by 17.2%and 4.4%,while the corrosion current density decreased by 87.2 and 80.9%,respectively.T4 treatment can greatly improve the corrosion resistance of composite materials,and T6 treatment can only improve its corrosion resistance slightly.When the aging time increases to a certain extent,it will weaken its corrosion resistance.The corrosion resistance of 2024alloy and its composites is mainly related to the size and shape distribution of S phase andθphase.Appropriate T6 treatment process can control the sensitivity of intergranular corrosion and pitting corrosion to a certain extent,and improve its corrosion resistance.