Preparation And Mechanical Properties Of Carbon Fiber Grafted Carbon Nanotube Reinforced Magnesium Matrix Composites

Carbon fiber reinforced magnesium matrix(C_f/Mg)composites has many advantages,such as light weight,high specific stiffness,high specific strength,low coefficient of thermal expansion and good dimensional stability.However,due to the smooth surface of the carbon fiber,the interface formed in composites is relatively flat,which makes it difficult to further improve the strength of the composite.According to researches,reducing the diameter of carbon fibers and increasing their aspect ratio may break the bottleneck.The appearance of carbon nanotubes(CNTs)has brought great hope for the preparation of high-performance magnesium matrix composites.But because of the strong Van der Waals'force,carbon nanotubes are difficult to be uniformly dispersed and easy to agglomerate,which has a negative impact on the reinforcing effect of the carbon nanotubes on the mechanical properties of the composite.Based on the above,a new idea of grafting carbon nanotubes onto the surface of carbon fiber by electrophoresis deposition technology was proposed to enhance the properties of magnesium matrix composites.Then the CNTs-grafted carbon fiber reinforced magnesium composites(CNTs-C_f/Mg)were prepared by the liquid-solid infiltration extrusion process independently developed by the research team.The influence of carbon nanotubes introduced by electrophoretic deposition on the properties of composites were investigated,and the optimum processing parameters were determined.The main contents of this paper are as follows:(1)The general experimental scheme of fabricating CNTs-C_f/Mg composites by electrophoresis deposition was proposed.The experimental device of electrophoretic deposition was established.The‘electrophoretic deposition,orthogonal layer,puncture stitching'process was proposed to preparing CNTs-C_f preforms.The experimental scheme for the preparation of the composites by liquid solid infiltration extrusion process was designed.Based on the universal electronic testing machine and the scanning electron microscope,the scheme of mechanical properties testing and microstructure observation of the composites were developed.(2)The influence of electrophoretic deposition parameters on the morphology of grafted carbon nanotubes was investigated.According to the basic principles of electrophoretic deposition,the main process parameters were determined.The changes of the process parameters were investigated.When the concentration of electrolyte was 1.0g/L,the concentration of carbon nanotubes was 1.5g/L and the time of electrophoresis was 40s,the morphology of carbon nanotubes grafted on the surface of carbon fiber was the most ideal.(3)The carbon nanotubes-carbon fiber preform(CNTs-C_f)was prepared through experiments.The influence of different process parameters of electrophoretic deposition on the content of carbon nanotubes was analyzed.The highest content of carbon nanotubes in the preform was 3.98 wt%.The key process parameters in the preparation process were determined.The CNTs-C_f/Mg composites with good infiltration and no obvious defects were prepared by liquid-solid infiltration extrusion process.(4)The effects of the introduction of carbon nanotubes on the mechanical properties of CNTs-C_f/Mg composites were discussed under different electrophoretic parameters.Compared with the C_f/Mg composites,the maximum tensile strength and flexural strength of CNTs-C_f/Mg composites were respectively increased by 68.11%and 62.75%.The carbon fiber was pulled out at the fracture surface of the specimen,which indicated the introduction of carbon nanotubes can improve the bonding interface to enhance the performance of the composite.(5)The influence of the content of carbon nanotubes on the mechanical properties of the composites was analyzed,and the best process plan is determined.Though analyzing the influence of the content of carbon nanotube in the preform on the properties of composite materials,the tensile strength and flexural strength of CNTs-C_f/Mg composites increased with the content of CNTs.The CNTs-C_f preform was prepared by‘electrophoretic deposition,orthogonal layer,puncture stitching'process.The optimum parameters were as follows:the electrolyte concentration was 1.0g/L,the concentration of carbon nanotubes was 1.5g/L,the electrophoresis time was 60s,preheat temperature and melting temperature is 605~615?,the infiltration temperature is 595~605?,the infiltration pressure is 30~40MPa,the holding time is 20~30min.Under the conditions of the process parameters,the CNTs-C_f/Mg composite fabricated by liquid-solid infiltration extrusion process was fabricated successfully and have the most outstanding properties.