Research On Microstructure And Properties Of CNTs/Mg-Zn Composites

Ingot castings of magnesium-zinc alloy with different content of carbon nanotubes were prepared by bell jar immersing precast block and mixing casting, and then wrought magnesium-zinc alloy with different content of CNTs were produced through extrusion deformation. The influence of the addition of carbon nanotubes on the microcosmic structure, the mechanical properties and corrosion resistance of the magnesium-zinc alloy which didn't contain aluminum were researched. The microstructure and grain size of the composites as-casting and as-extrusion were observed by using the optical microscopy, and analysed the influence of the CNTs addition on fining grains, the tensile strength testing machine was used to study the mechanical properties of the composites at room temperature, and analysed the effect of different adding amount carbon nanotubes on the tensile strength, elastic modulus, microhardness and elongation.Then the tensile fracture morphology characteristics of composites were observed by the scanning electron microscopy(SEM). The corrosion resistance and corrosion mechanism of the composites as extrusion was studied by means of the traditional weight-loss method, full immersion corrosion experiment and electrochemical corrosion polarization experiment.The results show that the CNTs can greatly refine the grains of magnesium-zinc alloy as cast condition and played a role of refining the two dendrite arm spacing and changing the crystal growth method. Then had fine grain structure(the most fine grain size about18.24μm) after extrusion deformation. The tensile strength, elastic modulus, microhardness and elongation of the magnesium-zinc with CNTs were enhanced. When the addition amount was1.0%, the maximum of tensile strength, elastic modulus, microhardness and elongation were219.740,43.6GPa,56.81HV and27%, and the increase of elongation was the most significant. The addition of Carbon nanotubes into magnesium-zinc alloy had good composite effect,and played a role of refining and strengthening the grain and grain boundary.So that the alloy had superior plasticity besides high strength. The fracture sections of the alloy mainly consist of dimples and prisms, which demonstrates toughness cleavage modes.Carbon nanotubes and matrix alloy combine tightly. The white whisker material in tensile fracture was the Carbon nanotubes whose surface was coated by matrix alloy. The addition of CNTs can significantly improve the corrosion resistance of composites. The corrosion weight-loss and average corrosion rate decreased as the increase of the addition amount of CNTs. When CNTs addition amount was2.0%and corroded72h, the weight-loss was only about31mg; when it corroded120h, the average corrosion rate were0.02664mg*cm-2/h, only about3/10as matrix alloy. PH value changing rule of corrosion solution and electrochemical corrosion experiments showed that the addition of carbon nanotubes can greatly improve corrosion resistance. The corrosion mechanism of carbon nanotubes reinforced magnesium-zinc composites was that carbon nanotubes distributed in the surface of the alloy as a reticulation, so that the two edge of crack was be effectively riveted and crack expanding was be prevented. At the same time the CNTs closely connected the matrix alloy with the oxidation film and had effect of reinforcement and then prevented detachment of oxidation film.