The grain density,Nv,in the solid state after solidification of AZ91/SiC composite is a function of maximum undercooling,ΔT,of a liquid alloy.This type of function depends on the characteristics of heterogeneous nucl...The grain density,Nv,in the solid state after solidification of AZ91/SiC composite is a function of maximum undercooling,ΔT,of a liquid alloy.This type of function depends on the characteristics of heterogeneous nucleation sites and number of SiC present in the alloy.The aim of this paper was selection of parameters for the model describing the relationship between the grain density of primary phase and undercooling.This model in connection with model of crystallisation,which is based on chemical elements diffusion and grain interface kinetics,can be used to predict casting quality and its microstructure.Nucleation models have parameters,which exact values are usually not known and sometimes even their physical meaning is under discussion.Those parameters can be obtained after mathematical analysis of the experimental data.The composites with 0,1,2,3 and 4wt.% of SiC particles were prepared.The AZ91 alloy was a matrix of the composite reinforcement SiC particles.This composite was cast to prepare four different thickness plates.They were taken from the region near to the thermocouple,to analyze the undercooling for different composites and thickness plates and its influence on the grain size.The microstructure and thermal analysis gave set of values that connect mass fraction of SiC particles,and undercooling with grain size.These values were used to approximate nucleation model adjustment parameters.Obtained model can be very useful in modelling composites microstructure.展开更多
To improve the surface properties of AZ91 magnesium alloy, Ni-SiC nanocomposite coatings with various SiC contents were pulse electrodeposited in modified Watts baths containing SiC nano-particles with the concentrati...To improve the surface properties of AZ91 magnesium alloy, Ni-SiC nanocomposite coatings with various SiC contents were pulse electrodeposited in modified Watts baths containing SiC nano-particles with the concentration of 0-15 g/L. The morphology of the coatings was studied by scanning electron microscope （SEM）. The SiC content of the coatings was measured by energy dispersive spectroscopy （EDS） analyzer. Microhardness measurement of the coatings showed up to 600% enhancement for the sample produced from the bath with 15 g/L SiC. The corrosion behavior of the coated AZ91 alloy was investigated by potentiodynamic polarization method. The results reveal a significant improvement in the corrosion resistance, that is, the corrosion current density decreases from 0.13 mA/cm2 for uncoated specimen to 1.74x10-6 mA/cm2 for the sample coated from the bath containing 15 g/L SiC and the corrosion potential increases from -1.6 V for uncoated specimen to -0.31 V for the sample coated from the bath. The wear resistance of both coated and uncoated samples was evaluated by pin-on-disc tribotester. The results show that the wear volume loss of coated sample is 8 times less than the bare alloy.展开更多
The influence of stirring parameters (stirring temperature, stirring speed and stirring time) on the particle distribution of 10%(volume fraction) SiC particulate reinforced AZ91 composites (SiCp/AZ91) was studied. It...The influence of stirring parameters (stirring temperature, stirring speed and stirring time) on the particle distribution of 10%(volume fraction) SiC particulate reinforced AZ91 composites (SiCp/AZ91) was studied. It is found that it is necessary for 10μm SiC particulate reinforced AZ91 composites to stir the molten composites in semi-solid condition with vortex formation, or else the cluster of the reinforcements would not be eliminated. Compared with the monolithic alloy, the SiCp/AZ91 composite has higher strength, especially for yield strength, but the elongation is reduced. For the as-cast composite, the particles often segregate within the grain boundary regions. Extrusion can effectively reduce the segregation of SiC particles and improve the mechanical properties of the composite. The extrusion-induced reduction in particle size varies with extrusion temperatures and extrusion ratios. The effect of extrusion-induced reduction in particle size on the mechanical properties of the composites is not always beneficial.展开更多
SiC nanoparticles reinforced magnesium matrix composites were fabricated by ultrasonic method.The AZ91 alloy and SiC nanoparticles with the average diameter of 50 nm were used as the matrix alloy and the reinforcement...SiC nanoparticles reinforced magnesium matrix composites were fabricated by ultrasonic method.The AZ91 alloy and SiC nanoparticles with the average diameter of 50 nm were used as the matrix alloy and the reinforcement,respectively.The addition of nanoparticles was 0.1%,0.3%,and 0.5%(mass fraction) of the composites.The results of microstructural evaluation and mechanical properties indicate that the nanoparticles can be dispersed into magnesium alloys efficiently and uniformly with the aid of ultrasonic vibration.As compared with the matrix alloys,the grains of composites were refined and the mechanical properties of composites were improved significantly.The SEM and DSC analyses show that the SiC nanoparticles can act as the heterogeneous nucleation of α-Mg.Also,the strengthening mechanism responsible for the composites reinforced with SiC nanoparticles was discussed.展开更多
基金supported financially by the European Community under Marie Curie Transfer of Knowledge grant No. MTKD-CT-2006-042468 (AGH No.27.27.170.304)Polish Ministry of Science and Higher Education for financial support under grant No. N507-44-66-34 (AGH No.18.18.170.325)
文摘The grain density,Nv,in the solid state after solidification of AZ91/SiC composite is a function of maximum undercooling,ΔT,of a liquid alloy.This type of function depends on the characteristics of heterogeneous nucleation sites and number of SiC present in the alloy.The aim of this paper was selection of parameters for the model describing the relationship between the grain density of primary phase and undercooling.This model in connection with model of crystallisation,which is based on chemical elements diffusion and grain interface kinetics,can be used to predict casting quality and its microstructure.Nucleation models have parameters,which exact values are usually not known and sometimes even their physical meaning is under discussion.Those parameters can be obtained after mathematical analysis of the experimental data.The composites with 0,1,2,3 and 4wt.% of SiC particles were prepared.The AZ91 alloy was a matrix of the composite reinforcement SiC particles.This composite was cast to prepare four different thickness plates.They were taken from the region near to the thermocouple,to analyze the undercooling for different composites and thickness plates and its influence on the grain size.The microstructure and thermal analysis gave set of values that connect mass fraction of SiC particles,and undercooling with grain size.These values were used to approximate nucleation model adjustment parameters.Obtained model can be very useful in modelling composites microstructure.
文摘To improve the surface properties of AZ91 magnesium alloy, Ni-SiC nanocomposite coatings with various SiC contents were pulse electrodeposited in modified Watts baths containing SiC nano-particles with the concentration of 0-15 g/L. The morphology of the coatings was studied by scanning electron microscope （SEM）. The SiC content of the coatings was measured by energy dispersive spectroscopy （EDS） analyzer. Microhardness measurement of the coatings showed up to 600% enhancement for the sample produced from the bath with 15 g/L SiC. The corrosion behavior of the coated AZ91 alloy was investigated by potentiodynamic polarization method. The results reveal a significant improvement in the corrosion resistance, that is, the corrosion current density decreases from 0.13 mA/cm2 for uncoated specimen to 1.74x10-6 mA/cm2 for the sample coated from the bath containing 15 g/L SiC and the corrosion potential increases from -1.6 V for uncoated specimen to -0.31 V for the sample coated from the bath. The wear resistance of both coated and uncoated samples was evaluated by pin-on-disc tribotester. The results show that the wear volume loss of coated sample is 8 times less than the bare alloy.
文摘The influence of stirring parameters (stirring temperature, stirring speed and stirring time) on the particle distribution of 10%(volume fraction) SiC particulate reinforced AZ91 composites (SiCp/AZ91) was studied. It is found that it is necessary for 10μm SiC particulate reinforced AZ91 composites to stir the molten composites in semi-solid condition with vortex formation, or else the cluster of the reinforcements would not be eliminated. Compared with the monolithic alloy, the SiCp/AZ91 composite has higher strength, especially for yield strength, but the elongation is reduced. For the as-cast composite, the particles often segregate within the grain boundary regions. Extrusion can effectively reduce the segregation of SiC particles and improve the mechanical properties of the composite. The extrusion-induced reduction in particle size varies with extrusion temperatures and extrusion ratios. The effect of extrusion-induced reduction in particle size on the mechanical properties of the composites is not always beneficial.
基金Project(2007CB613706) supported by the National Basic Research Program of ChinaProject(00900054R4001) supported by Innovation Project for Talents of BJUTProject(00900054K4004) supported by the Science Foundation for Youths of BJUT
文摘SiC nanoparticles reinforced magnesium matrix composites were fabricated by ultrasonic method.The AZ91 alloy and SiC nanoparticles with the average diameter of 50 nm were used as the matrix alloy and the reinforcement,respectively.The addition of nanoparticles was 0.1%,0.3%,and 0.5%(mass fraction) of the composites.The results of microstructural evaluation and mechanical properties indicate that the nanoparticles can be dispersed into magnesium alloys efficiently and uniformly with the aid of ultrasonic vibration.As compared with the matrix alloys,the grains of composites were refined and the mechanical properties of composites were improved significantly.The SEM and DSC analyses show that the SiC nanoparticles can act as the heterogeneous nucleation of α-Mg.Also,the strengthening mechanism responsible for the composites reinforced with SiC nanoparticles was discussed.
