Study On Microstructure And Properties Of AZ91 Magnesium Matrix Composite Reinforced By High Temperature Carbon Nanotubes

Carbon nanotubes(CNTs)are the excellent reinforcements of magnesium matrix composite due to their fantastic mechanical properties,such as high strength and high modulus.How to obtain the well-dispersion of carbon nanotubes in matrix is the key to the preparation of high performance composite materials.The effect of improving the purity of original CNTs on mechanical properties of magnesium matrix composites was investigated.In this work,Graphitized-CNTs/AZ91 magnesium matrixcompositeswerepreparedbypowdermetallurgyprocess.The graphitized-CNTs reinforced magnesium matrix composites with content of 0wt.%to5wt.%were successfully prepared by powder metallurgy method.The graphitized CNTs was characterized by Fourier transform infrared spectroscopy(FTIR),Raman spectroscopy(Raman Spectrometer),X ray diffraction,scanning electron microscopy and transmission electron microscopy.The grain size of Graphitized-CNTs/AZ91magnesium matrix composites with different contents was calculated by using Image Pro-Plus 6.Microhardness tester was used to test the microhardness of the composites in the sintered and extruded states.The mechanical properties of the composites were tested by the tensile specimen machine.The fracture morphology of the tensile sample was observed with SEM.The effects of different content of Graphitized-CNTs on the microstructure and mechanical properties of AZ91 alloy were studied.The main contents are summarized as follows:(1)The raw CNTs was treated at 3000 degree graphitization by high temperature treatment.According to the analysis of infrared spectral data,the peak value of graphiradiograph-cnts was basically unchanged compared with the original CNTs,and the structural integrity of CNTs was not damaged by high temperature treatment.The results of XRD show that the intensity of the characteristic peak of C(002)surface of Graphitized-CNTs increases obviously(nearly doubled),the half width and width decrease,showing a more sharp form,and the arrangement of Graphitized-CNTs is more complete and orderly.Raman spectra show that the I_D/I_G ratio of CNTs without high temperature graphitization is 1.49.The I_D/I_G ratio of CNTs after high temperature graphitization was obviously reduced(0.57).The graphitization treatment greatly improved the defect of CNTs.The CNTs D peak and G peak of graphitization did not shift frequency,indicating that the high temperature treatment did not change the diameter of the CNTs.It was observed by TEM that the atomic arrangement of the Graphitized-CNTs tube was very neat,and the catalytic particles and metal particles were basically removed,indicating that the high temperature treatment could improve the purity of CNTs.(2)Graphitized-CNTs can refine the grain size of magnesium matrix organization(sintering state and squeezed state composites),added different content of Graphitized-CNTs on the average grain size of the composite material with different degree of influence,can make the grain size of compound material changes,along with the increase of the content of CNTs composites is the size of the average grain size is the trend of increase with the decrease of the first.Image pro-plus 6.0was used to calculate the average grain size of the sintering state of the composite material,which was 81.6um,76.8 um,72.8 um,66.3 um,73.9 um and 83.7 um respectively.The average grain size of the extruded state is 41.2 um,32.6 um,30.6um,19.6 um,21.8 um and 28.6 um respectively.The addition of Graphitized-CNTs enhances the effect of grain refinement.When the addition of Graphitized-CNTs is3wt.%,the average grain size of the sintered and extruded composites reaches the minimum,and the microhardness of the composites reaches the maximum at this time.The average grain size of magnesium matrix composites is smaller than that of the matrix.With the addition of reinforcement,the change rule of microhardness of composites increases first and then decreases.(3)The addition of Graphitized-CNTs has a certain influence on the yield strength and elongation of the composite,that is,the mechanical properties of the composites increase first and then decrease with the increase of the content of the reinforced body.When the amount of Graphitized-CNTs in the matrix is 3.0wt%,the Graphitized-CNTs/AZ91 composite materials tensile strength,yield strength and elongation is 230 MPa and 219 MPa and 0.9%,respectively.Compared with the matrix decreased by 16.4%,16.4%and 3.1%respectively.Compared with the original CNTs reinforced magnesium matrix composites,the mechanical performance index was reduced by 12.4%,25.6%and 79.9%,respectively.Compared with MgO@CNTs reinforced magnesium matrix composites,the corresponding mechanical performance indexes were reduced by 30.5%,22.8%and 89.5%respectively.