| Magnesium and its alloys are very promising lightweight metal structurematerials owing to their excellent properties. In recent years, with the constantdevelopment of the industry, requirements on the properties of magnesium alloy aremore and more stringent, and a series of high performance magnesium alloys, likehigh-strength magnesium alloy, ignition-proof magnesium alloy and heat-resistant magnesium alloy, were developed. Meanwhile, many fields need a hightradeoff performance on the strength, plasticity, heat resistant and corrosion resistant,etc. The research and development on new type of magnesium alloys and compositeswith excellent comprehensive properties have important significance. In this paper,in order to further improve the comprehensive properties of magnesium alloy,Mg-Mn-Ce-Zn composites reinforced with CNTs are fabricated by stirring castingprocess. The microstructure, mechanical properties, corrosion resistance and hotdeformation behavior have been characterized in metallographic microscope, energydisperse spectroscopy(EDS), scanning electron microscopy (SEM), transmissionelectron microscopy(TEM), differential scanning calorimeter(DSC), electrochemicalanalysis, thermo-simulated test and so on. In addition, the toughening mechanism,corrosion resistance mechanism, fracture mechanism,and rule of microstructurevariety of hot deformation process are also discussed. First of all, microstructure, mechanical properties, ageing behavior andcorrosion resistance of CNTs/Mg-1.3Mn-1.0Ce-4.0Zn composites are studied. Theresearch on the microstructure and mechanical properties show that with the increaseof CNTs'contents, grains of Mg alloy are obviously refined. Meanwhile, the grainmorphology and distribution characteristics of second phase are changed. Theas-cast grain has transformed equiaxed shape to dendritic shape. And the number ofsecond phase increases simultaneously. With the increase of CNTs'contents, thetensile strength and elongation both increase firstly and then decrease dramatically.Actually,0.5%CNTs/Mg composites exhibite the highest tensile strength andelongation (212.2MPa and 21.1%, respectively),+8.5%and+37.5% higher than pureMg alloy's respectively. The study of ageing behavior shows that with the content ofCNTs, the peak-age hardness of samples is correspondingly improved, and the timefor peak-aged is shortened. Potentiodynamic polarization curves investigate thatthe addition of CNTs resulted in higher corrosion potential of the electrode and obviously accelerate the corrosion current density. The corrosion resistance is improved.Second, hot compression test of CNTs/Mg-1.3Mn-1.0Ce-4.0Zn composites has taken on Gleeble-3500 thermal simulated test machine. Through analysis hot deformation behavior of the composites, deformation temperature and strain rate are the key factors that affect the rheological stress. The flow stress model of composites in the hot forming process are expressed by hyperbolic sine equations containing Z(Zener-Hollomon)parameter. The values of parameters of stress exponents n and deforming activation energies Q are 9.23 and 207.19kJ/mol, respectively, far above the values of pure magnesium's. Research on the microstructure of composites in different hot deformation conditions has shown that the deformation temperature and strain rate are the main factors which affects the grain size and microstructure of composites. When hot compression at lower temperature(200?250?), the deformed microstructure is composed primarily of fiber texture and twin crystals. The interwoven degree of the twin crystals increases with the increase of strain rate. When hot compression at higher temperature (300?400?), dynamic recrystallization occurs in the microstructure. With the increase of strain rate, the degree of recrystallization increases, and the grain size decrease. A fine and uniform, equiaxed grain structure is obtained when the temperature is 400? and the strain rate is 10s-1. |
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