Effect of strain rates on mechanical properties, microstructure and texture inside shear bands of pure magnesium

Abstract

In the paper, mechanical properties and microstructure of pure Mg hat-shaped samples after dynamic impact and quasi-static compression were studied. Results showed that the maximum peak strength 241.46 MPa and yield strength 51.65 MPa at 1.8 × 104 s−1 were obtained, and strain rate sensitivity and hardening rate under dynamic impact were much higher than those under quasi-static compression. Grains in matrix region kept the size of the original grains, and the 〈0001〉 direction was parallel to the loading direction. A strong texture appeared within the shear bands, and the maximum intensity between 15 and 21 increases as increasing strain rate. The <0001> direction of most grains with the sizes between 3 and 4.5 μm, in general, was perpendicular to shear band direction or shear direction. {10−12} 〈10−11〉 tension twins played an absolute leading role in twins, while the fraction of other types of twins was negligible. The temperature within adiabatic shear band (ASB) reached the maximum value of 376 K at 1.8 × 104 s−1, and the maximum absorbed energy density (ΔE) of 226.37 MJ·m−3 also was obtained. The average ASB widths between 87 and 135 μm decreased with increasing strain rate, and the trend was the same with that predicted by Bai-Dodd model. Dynamic recrystallization (DRX) grains slip and rotate under the action of normal stress Fn, and form ASB together. Fracture occurred along shear band, and brittle fracture characterized by cleavage surface and ductile fracture characterized by dimples both existed during the fracture progress.