The dynamic compression behavior of AZ31B magnesium alloy with hat shaped specimen was investigated at high strain rate in this paper. Based on the Johnson‐cook constitutive model and fracture model, the interaction of temperature, stress and strain fields of AZ31B magnesium alloy with hat shaped specimen were numerically simulated by using ANSYS/LS‐DYNA software under different strain rates, which was validated by experiment. It is found that the plastic strain is highly concentrated on the corner of the hat shaped specimen, which leads to large localized deformation. The voids are nucleated and extended by compression stress. Work harden effect is caused by remained plastic strain, which is located around adiabatic shear band. The stress collapse is discovered in gauge section, which is also discovered in experiment. Thermal soften effect is suppressed with the strain rate increased.
The quasi‐state and dynamic mechanism of AZ31 magnesium alloy at a strain rates range of 0.001 s‐1–2500 s‐1 under a temperature range of 20 °C–250 °C were researched by compression tests using the electronic universal testing machine and split Hopkinson pressure bar system. The true stress‐strain curves at different strain rates and evaluated temperatures were obtained. The result shows that the thermal soften effect of AZ31 magnesium alloy is significant. By modifying the temperature term of the original Johnson Cook model of AZ31 magnesium alloy, a modified Johnson Cook model of AZ31 magnesium alloy has been proposed to reveal thermal soften effect on the deformation behavior of AZ31 magnesium alloy more precisely. With the modified Johnson Cook model and fracture model, the finite element method simulation of AZ31 magnesium alloy hat shaped specimen under impacting was conducted. The numerical simulation result is consistent with the experimental result, which indicates that the modified Johnson Cook model and fracture model are greatly valid to predict the deformation and fracture behavior of the AZ31 magnesium alloy hat shaped specimen under impacting.
The rapid solidification experiments have been carried out for the Nb(45‐x)YxNi55 (x = 9, 19, and 27) alloys. The microstructure characterization shows the occurrence of the liquid‐liquid phase separation into the Niobium‐rich and Yttrium‐rich liquids. The Niobium‐rich spherical particles were embedded in the glassy Yttrium‐rich matrix for the alloy Nb36Y9Ni55, while glassy Yttrium‐rich ones were located in the glassy Niobium‐rich matrix for the alloy Nb18Y27Ni55. A structure of hierarchical separation was detected in the as‐quenched alloy Nb26Y19Ni55. The size distribution of the spherical particles in the as‐quenched Nb(45‐x)YxNi55 (x = 9 and 27) alloys ranges from several nanometers to sub micrometer and is close to the Gaussian distribution. The average diameters of the Niobium‐rich particles in the as‐quenched Nb36Y9Ni55 alloy and the Yttrium‐rich particles in the Nb18Y27Ni55 alloy are 0.23 μm and 0.15 μm, respectively. A dual‐glass structure in the as‐quenched Nb18Y27Ni55 alloy ribbon was determined by X‐ray diffraction and transmission electron microscopy.
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