Microstructure evolution of extruded Mg-Gd-Y magnesium alloy under dynamic compression

Abstract

For the purpose of investigating the microstructure evolution and deformation behavior of magnesium under high strain rates, the Split Hopkinson Pressure Bar (SHPB) apparatus was used under high strain rates from 755 s −1 to 2826 s −1 in the present work at room temperature. The microstructures of extruded Mg-Gd-Y Magnesium alloy under different strain rates and along different compression directions were observed by metallographic microscope. The results show that, microstructures of extruded Mg-Gd-Y Magnesium alloy along ED, TD and ND compression directions are sensitive to strain rates. The amount of twins firstly increases and then decreases with strain rates being increased, and the recrystal grains increase and grow up. When the strain rate reaches 2500 s −1 , the adiabatic shear band (ASB) begins to form. The formation process of the adiabatic shear band can be divided into three stages. In the first stage, under the impact load a great deal of twins form and the deformation mechanism is twinning. In the second stage, discontinuous ASB forms due to twins adjusting the directions of located grains and the deformation mechanisms are twinning and non-basal slip. In the last stage, non-basal slip turns to basal slip and continuous ASB forms. The dynamic compression fracture mechanism of extruded Mg-Gd-Y Magnesium alloy is multi-crack propagation.