Research On Thermal Stability And High Temperature Properties Of Magnesium Matrx Composites Reinforced With Carbon Nanotubes

Carbon nanotubes (CNTs) were uniformly distributed in magnesium alloy (AZ80)by friction stir processing (FSP). The thermal stability of composite was tested atroom temperature, high temperature.The microstructure and fracture morphology ofcomposite materials were observed by OM, SEM, TEM. The thermal stabilityperformance and internal mechanisms of composite were discussed under differentenvironment, which provided the theoretical foundation for the promotion ofmagnesium composite materials in the high temperature field.The results show that: while the microstructure of the central area of FSPedmagnesium matrix were fine equiaxed grain without observe significant defects. Atroom temperature, the tensile strength of composites was improved as the CNTscontent increasing. At high temperature, the tensile strength of the composite wasreduced and decreased faster as the temperature increasing. However, the tensilestrength of the composite was improved as the content of CNTs increasing. In heatexposure conditions, the tensile strength of composites decreased as the temperatureof heat exposure increasing or the content of CNTs decreasing. The hardness ofcomposites at room temperature increased as the amount of CNTs increasing, but inheat exposure conditions, the hardness of composites were increased first and thendecreased. when the temperature of heat exposure reached to250℃, the highesthardness was got.Fracture observations show: at room temperature, the micro-fracture mode ofcomposites was ductile fracture, however, the plasticity of composites decreased ascomparing with the base metal. When the strain rate of the strength test was low athigh temperature, the binding force of the interface of CNTs and magnesium matrixenhance the strength of composite, which reduced the strength of composite. In heatexposure conditions, when the thermal exposure temperature was lower than250℃,CNTs limited the movement of dislocation; when temperature was more than250℃, a great number of second phase precipitates appeared in the form of aggregationof blocks, which made the composites failure.