| Magnesium and Magnesium alloy has the advantages of abundant reserves, high recovery rate, easy cutting, strong anti deformation ability, light weight and so on. With the need of the modern society, magnesium alloy was more and more widely used in engineering application. The AM50 itself has good comprehensive mechanical properties. After adding a small amount of rare earth element Nd, the strong toughness will be further improved. It can be used for the steering wheel of automobile or other parts. At present, the research on the mechanical properties of AM50 was mostly carried out under static conditions, In the process of collision, the dynamic mechanical properties of the material were required to understand the dynamic mechanical properties of the material in high strain rate. However, there are not much data of the deformation behavior of magnesium alloy at high strain rate, So it was important to study the microstructure evolution, deformation and fracture behavior of AM50 and AM50-Nd magnesium alloy under high strain rate.In this paper, the dynamic mechanical properties of AM50-Nd magnesium alloy were analyzed by means of the experimental device of Hopkinson pressure bar test. The dynamic mechanical properties of AM50-Nd magnesium alloy were analyzed by means of obtaining the stress and strain data. The constitutive equation of AM50 magnesium alloy was obtained by using the least square method. By fitting the parameters of the constitutive equation, the data obtained from the experiment were verified by ANSYS software, and the constitutive equation of AM50 magnesium alloy in the range of 500s-1-3000s-1 was obtained. And with the increase of the strain rate, and there is no obvious yield point, which reflects the positive strain strengthening effect of the alloy and the continuous yield, At the same time, the influence of strain rate on the flow stress of the material is more and more small. With the increase of Nd content, the fracture stress gradually increases, and the fracture strain decreases gradually. AM50-Nd magnesium alloy’s fracture failure mode is the ductile to brittle fracture under quasi-static and at high strain rate the fracture mode is quasi cleavage fracture, with the increase of strain rate the fracture mode change gradually from ductile to brittle fracture gradually to the cleavage fracture mode transition; At room temperature, with the increase of Nd content, the grain refinement, the adiabatic shear sensitivity of the material is enhanced.The microstructure characteristics of Nd magnesium alloy under high speed impact of AM50 magnesium alloy were explored by optical microscope (OM). By optical microscopy to explore the different Nd content of AM50 Magnesium Alloy in high speed impact process of material deformation microstructure characteristics; By scanning electron microscope (SEM) of AM50-Nd magnesium alloy at high strain rate impact specimen fracture morphology was observed to analyse the AM50-Nd magnesium alloy deformation behavior and fracture mechanism, found that increasing the content of Nd will increase AM50 magnesium alloy fracture to cleavage mode trend in the same strain rate.With the numerical simulation of high speed deformation mechanism of AM50 magnesium alloy, we study on the concentration of local stress and the fracture behavior of materials under high speed impact load:when the load reach the failure limit of unit, there will formate dead pixels, gradually extend along the axis direction of 45 DEG to the form of crack in the propagation of shear bands which were put forward according to the fracture mechanism of AM50-Nd magnesium alloy:Firstly the microvoids will be formed in the adiabatic shear zone, than the microvoids grew up, elongated, be connectied, and eventually form a crack. |
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