Study On Preparation And Mechanical Behavior Of Mg Alloy Based Hybrid Nanocomposites

As a new kind of nano-composite, magnesium alloy composites reinforced with nanoparticles and nanofiber, have drawn increasing academic attention at home and abroad in recent years because of their excellent mechanical properties. Study on mechanical properties and influencing factors as well as strengthening mechanisms will obviously expand application of magnesium alloy in the aerospace, chemical, automotive, biomedical and other fields.In this paper, AZ91 magnesium alloy based composites reinforced with different mass ratio of carbon nanotubes(CNTs) and SiC nanoparticles were prepared by the self-designed ultrasonic stirring casting technique. The total adding amount of the hybrid reinforcements is 1% mass fraction of AZ91. By using X-ray diffraction(XRD), optical microscopy(OM), scanning electron microscopy(SEM), Transmission electron microscopy(TEM), tensile testing machine, four-ball friction machine and high temperature creep testing apparatus, The effects of hybrid nano-powder on microstructure and mechanical properties of AZ91 magnesium alloy were studied, and their effecting mechanisms were also discussed.The experimental results show that Mg alloy based hybrid nanocomposites with high interface binding strength and well-dispersed nano-hybrid reinforcements cab be prepared by using high-intensity ultrasonic treatment process. The mechanical properties of the composites are greatly improved. Comparing with AZ91 magnesium alloy, the tensile strength and elongation of the composites increase by 50% when the hybrid ratio of CNTS and nano-sized SiC particles is 7:3, while the brinell hardness of the composites increase by 30% when the hybrid ratio of CNTS and SiC is 5:5. In addition, the high temperature creep and wear resistance are both improved to some extent. However, when CNTs and nano-SiC addition are higher, the mechanical properties may be degenerated greatly.A 3D hybrid cell model of the composites is developed in the present paper, and the stress field and stress-strain relationships are calculated with finite element software LS-DYNA, the computational results are compared with the experimental data. Because of the presence of nano-sized hybrid reinforcements, the crystal grain are refined and dislocation increased, resulting in the improved performance of magnesium alloy composites. Finally, defects during casting such as shrinkhole, shrinkage, thermal crack can be directly predicted on the basis of the temperature and stress field calculated by casting CAE soft. Accoring to the results, process optimization and improvement can be carried out. In this way, quality of casting can be improved, production cycle can be shorten and production cost reduced. This can provide theoretical guidance for the application of magnesium alloy.