Microstructure evolution of adiabatic shear bands in AM60B magnesium alloy under ballistic impact

Microstructure evolution of adiabatic shear bands (ASBs) in AM60B Mg alloy impacted by a GCr15 projectile at a velocity of 500 m s-1 was studied through optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the deformed and transformed bands were formed around the crater, and the transformed bands under different etchants presented different responses, which indicated that the etching color to distinguish transformed bands was inaccurate. The ultrafine and equiaxed dynamic recrystallized grains in the transformed bands were confirmed, and twinning-induced rotational dynamic recrystallization mechanism was proposed to be responsible for the formation of the ultrafine grains in the bands. Microhardness measurements show that the microhardness in the bands was two times higher than that of the matrix, which should be attributed to the strain hardening and grain refining.