The Research Of Carbon Nanotubes-reinforced AM60 Magnesium Matrix Composites

Ni-coated carbon nanotubes(Ni-CCNTs)/AM60 composites and Ni-CCNTs/Mg-1 Zn-0.25Mn-xAl(0,1,3,5,8,10)composites were fabricated by stirring casting method under the protection of Ar.The mechanical properties of the composites which were under the state of as-cast and high temperature were tested.The microstructure was investigated with optical microscopy and tested by x-ray diffraction.The fractography characteristics of the composites were observed by scanning electron microscopy(SEM) and energy spectrum analysis(EDS).The effect rules of room-temperature mechanical properties and elevated temperature properties of composites when enhancing the mass fraction of Ni-coated CNTs addition were investigated emphatically. At the same time, the change of microstructure was studied.The results showed that: the addition of Ni-coated CNTs could significantly enha- nce the mechanical properties of Ni-CCNTs/AM60 composites, the rules of which were always enhancing, then reaching the maximum, and dropping at last.Under the state of as-cast, when the addition of Ni-coated CNTs was 1.0wt%, the tensile strength, micro- hardness and the ductility reached the maximum,while the addition of Ni-coated CNTs were 1.2wt%, the elastic modulus reached the peak value respectively.Under the state of high temperature, the tensile strength declined remarkably, and the ductility enhanced. When the addition of Ni-coated CNTs were 1.2wt% and 0.8%, the tensile strength and the ductility all reached the maximum, which is 34.90% and 76.73% more than the value of the matrix respectively. Ni-coated CNTs could not only refine the grains of the composites, but also overlap the grains and bear the load of resistance to deformation. The fracture mode of composites mainly consisted of the dimple and the tear edge, which showed the feature of gliding fracture. When the addition of Ni-coated CNTs and Zn was 1.0%, At ordinary temperature, the tensile strength of the Ni-CCNTs/Mg -1Zn-xAl composites increased with the increase of the content of Al first, then reaching the maximum, and dropping at last, but the microhardness increased all the time. At high temperature the rule of tensile strength to the aluminum addition are similar to that of room-temperature, while the ductility declined all the time.With the increase of Al content, the Initial Phaseα-Mg declined, while the strengthening phase Al₁₂Mg₁₇ incr- eased and distributed more continuously, and also, the grain size decreeases obviously.