Microstructure, texture, and fracture of pure magnesium adiabatic shear band under high strain rate compression

In the paper, the microstructure and texture of adiabatic shear band (ASB) in hat-shaped pure magnesium specimens under dynamic shear loading were investigated, and the formation and fracture mechanism of ASB were discussed as well. Results showed that, the straight ASB, with a width about 90 mu m was formed upon shear loading, being consisted of the transition and ASB central regions. Equiaxed grains with large angle grain boundaries (LAGBs) were deposited in the ASB central region, and had a size distribution ranging from 0.3 to 3.0 mu m. From ASB central to matrix regions, grains and strain both increased, and strain concentration occurred in matrix region. 0001 direction of the grains in matrix and transition regions was parallel to the loading direction (LD), while that of the grains in ASB central region was perpendicular to the shear band direction (SBD). The mechanically-driven subgrain rotation model provides a reasonable explanation for the texture in ASB. Dynamic recrystallized (DRX) grains slip and rotate under normal stress, resulting in (0001)//SBD texture with the maximum pole intensity of 16.73. Due to the high stress at the triple junction of grains boundaries, voids appear, and the formation and combination of voids lead to secondary and main cracks. Finally, the main crack propagates rapidly along the interface between central region and transition region, and then fracture occurs along ASB with a mixed fracture mode of brittle and ductile fracture.

Automated summary

The study reveals that under dynamic shear loading, a straight ASB is formed in pure magnesium specimens, consisting of transition and central regions with equiaxed grains containing large angle grain boundaries. Grain and strain increase from ASB central to matrix regions, resulting in strain concentration in the matrix region. The mechanically-driven subgrain rotation model explains the texture in ASB, showing dynamic recrystallized grains slip and rotate under normal stress, leading to a mixed fracture mode of brittle and ductile fracture along the ASB.