Electropulsing anisotropy of pre-twinned AZ31 Mg alloy: A quasi-in-situ EBSD analysis

The electropulsing anisotropy of pre-twinned AZ31 Mg alloy was investigated via quasi-in-situ electron backscatter diffraction analysis to decouple the thermal and athermal effects of electropulsing treatment. A pre-compression along the rolling direction (RD) introduced extensive {10−12} extension twins, yielding a twinned area fraction of 75.4%. Three consecutive electropulses were applied along the RD or the transverse direction (TD), with the durations tailored to maintain comparable peak temperatures. The TD specimens exhibited higher heating efficiency owing to the predominant a -axis current path preserved in both matrix and twinned regions despite twinning-induced lattice rotation. A finite difference simulation based on the c -axis orientation distribution predicted an electrical resistivity ratio in excellent agreement with the experimental value. Quasi-in-situ tracing revealed that strain-induced boundary migration governed the early stage of microstructural evolution, while nucleation and growth gradually became activated during subsequent cycles; thermally activated twin boundary migration was suppressed under the subsecond thermal exposure. Notably, the RD specimens underwent faster grain growth and twin boundary annihilation than the TD counterparts, contrary to predictions based on grain morphology and texture. This anomalous behavior was ascribed to current crowding in the twinned regions, where the lower resistivity along the c -axis locally amplified the athermal effect, as evidenced by preferential static recovery under a short-duration electropulse. The RD specimens recovered more ductility (up to 71%) than the TD counterparts (19%). This ductility recovery was governed primarily by the deformation behavior associated with the tensile direction and further enhanced by the accelerated microstructural evolution in the RD specimens, which delayed the onset of plastic instability.