Study On Microstructure And Properties Of Carbon Nanotubes Reinforced Magnesium Matrix Composites By Friction Stir Processing

Multi-walled Carbon nanotubes reinforced magnesium matrix (MWCNTs/Mg)composites with the volume fraction of1.1%to7.1%were fabricated by friction stirprocessing (FSP). The effect of the Processing times and MWCNTs content on Macromorphology and microstructure was analyzed, The uniformity of MWCNTsdistribution in the composite were tested, The effect of mechanics properties andcorrosion resistance was studied, And used scanning electron microscope to observemicrostructure, To combine with the above conditions, microwave absorbingproperties and electromagnetic shielding of the composites was investigated.The results of research show that: The MWCNTs are distributed uniformly anddensity when the processing times was5times. And when the content of Multi-walledcarbon nanotubes is1.1%~3.9%, the molding of composite materials is better. As thecontent of MWCNTs is increasing, the recombination region appears an area ofgrowing black patches. The reason for that just segregation of MWCNTs. thedistribution of MWCNTs is analyzed in the composites, In Center of friction stir zonethe distribution is uniform, but the phenomenon of segregation is especially obviousin the edge of friction stir zone.The microstructure of composite material has been refined when it addMWCNTs in it. When the content of MWCNTs is increasing, the averagemicro-hardness of composite materials is obviously improve, the trend of tensilestrength of composites material rised at first, but after that it decline, the elongationdrop gradually. the fracture surface of MWCNTs0/Mg composite material revealdimples and tear ridge, it is hybrid fracture that combine brittle fracture and ductilefracture; when the content of MWCNTs is5.7%, the tensile strength of composite is1.35times than before, and the fracture of composites is brittle fracture. When thecontent of MWCNTs is increasing, the the reunion of MWCNTs is increasing, whichaffect the MWCNTs and the magnesium matrix interfacial bonding strength, and it notonly cause crack propagation but also it has an effect on bonding strength. thecorrosion resistance of composites materials is improved, the average of corrosionrate of composites change from4.1478mg (m2s)-1to1.5679mg (m2s)-1, Andcorrosion potential(Ecorr) which become larger gradually, and the corrosion current decreases, meanwhile, the charge transfer resistance is increased, So the corrosionresistance of composites materials is better than base material, With increasing thecontent of MWCNTs can be reinforced the surface oxide layer of composites material,and it prevents the formation of corrosion cracks and infiltration of corrosive liquid.The research of MWCNTs/Mg composites on absorption of electromagneticwaves and shield indicates that: the addition of MWCNTs, composite materials onabsorption of electromagnetic wave is not improved, with increasing the frequency,the microwave absorptivity of composites decrease in the frequency range of2GHz~18GHz, The reflection loss of metal matrix is greater than the absorption lossof MWCNTs. the reflection loss increase which is good for material to shieldelectromagnetic wave. the electromagnetic shielding effectiveness of MWCNTs/Mgcomposite is less than-85dB in the lower frequency range of0.1MHz~3GHz, Withincreasing the content of MWCNTs, the conductivity of composite materials decreaseand the electromagnetic shielding slightly increase.