Preparation And Properties Of High Strength And Ductility Layered CNTs/Mg Composites

In order to solve the mismatch between strength and ductility of Mg matrix composites,carbon nanotubes（CNTs）can be introduced as reinforcements.However,it is difficult to prepare composites with CNTs uniformly dispersed in Mg matrix by traditional methods.In this paper,CNTs/Mg layered units was prepared by electrophoretic deposition（EPD）,and then layered CNTs/Mg composites were prepared by spark plasma sintering（SPS）at different temperatures.The deposition morphology of layered units obtained by EPD and the microstructure,mechanical properties and damping properties of the composites were analyzed.The main research contents and results are as follows:The CNTs were acidified with mixed acid（concentrated H₂SO₄:H₂O₂=7:3）,and the CNTs/Mg layered units was prepared by EPD process.Scanning electron microscope（SEM）observation of the layered elements prepared for different electrophoretic deposition parameters（different deposition time and voltage）shows that the better deposition effect is that the CNTs on the layered units are uniformly distributed over the surface of the Mg substrate without agglomeration.When the deposition voltage is 300V,the deposition time is 0.5,1,and 1.5min,and when the deposition voltage is 350V and the deposition time is 0.5,1,and 1.5min,the deposition effect is relatively good.Layered pure Mg and CNTs/Mg composites were prepared by SPS sintering.The effect of sintering process of microstructure and properties was studied.It was found that the bonding between layers was close.The tensile test results:when sintered at 600℃and kept at room temperature during furnace cool,the tensile strength and elongation of CNTs/Mg composites was increased by 8.3%and 15%respectively compared with pure Mg.Whether the pressure is maintained during the cool process has an important impact on the mechanical properties.When the sintering temperature is 600℃,the tensile strength of the samples of pressure is reduced by17.6%and the elongation is increased by 24.4%.Different sintering temperatures will also affect the mechanical properties.Sintering at 590℃and 600℃and keeping the pressure at room temperature when cool with the furnace,the tensile strength and elongation of the samples of 590℃is increased by 8.0%and 65.6%respectively.Therefore,different sintering processes have an important impact on the properties of layered CNTs/Mg composites.The damping properties of layered pure Mg and CNTs/Mg composites were tested by dynamic mechanical thermal analyzer.The results show that the damping properties of CNTs/Mg composites are lower than those of pure Mg,which are reduced by 35.8%and 34.4%at room temperature（30℃）and high temperature（250℃）respectively.The damping test temperature curve of CNTs/Mg composites increases gradually to the increase in temperature in the range of room temperature-350℃,and there are two internal friction peaks.At room temperature,the damping properties of the composites decrease with the increase in frequency.The damping performance of the composites increases in the increase in strain amplitude,only when the strain amplitude is 20×10^-6m,the damping performance decreases.