<p>High-speed impact tests at a strain rate of 3300&#xa0;s⁻¹ were performed on Mg–Al-Mn alloys using a split Hopkinson pressure bar (SHPB), with loading applied along both the extrusion direction (ED) and transverse direction (TD). A cutoff ring was used to control strain, enabling detailed characterization of microstructural evolution and adiabatic shear behavior. Compared with quasi-static loading, high strain rates significantly enhanced twinning activity. After 2% strain in both ED and TD, deformation was dominated by twin growth rather than nucleation. Under TD loading, adiabatic shear bands (ASBs) formed at 12% strain, showing pronounced localization and leading to premature failure. Experimental observations, supported by theoretical calculations, demonstrated that the TD direction exhibited higher adiabatic shear sensitivity than the ED direction, resulting in stronger softening, lower ultimate compressive strength, and earlier onset of failure. Despite the short deformation time at high strain rates, discontinuous dynamic recrystallization (DDRX), continuous dynamic recrystallization (CDRX), and twin-induced dynamic recrystallization (TDRX) were identified as the primary mechanisms contributing to ASB formation. These findings provide new insights into the root causes of ASB-induced failure in magnesium alloys and suggest pathways for texture design and microstructural control strategies to improve their reliability in engineering applications.</p> Graphical abstract <p></p>