Multiscale heterostructure optimization in Mg–Pb–Al–B-Sc alloys: achieving strength-ductility balance via EX-ECAP and Sc alloying

Mg–Pb–Al–B-Sc (MPAB-xSc, x = 0, 0.5, 1.5 wt%) alloys have good nuclear radiation shielding performance, but the abundance of brittle secondary phases leads to strength-ductility trade-off. To overcome this limitation, this work adopts deformation engineering principles via extrusion-equal channel angular pressing (EX-ECAP) to architecturally transition the microstructure from multimodal (coarse/fine/ultrafine grains) to a refined bimodal (fine/ultrafine grains) structure. Sc alloying combined with EX-ECAP activates non-basal slip systems, inducing significant texture reorientation. Schmid factor analysis confirms the dominance of prismatic and pyramidal slip mechanisms, evidenced by substantially increased non-basal slip activity. Concurrently, the increase in Al 3 Sc phase fraction and severe plastic deformation promote dislocation accumulation, facilitating recrystallization nucleation. Higher Sc content shifts dynamic recrystallization (DRX) behavior toward continuous dynamic recrystallization (CDRX), suppressing discontinuous dynamic recrystallization (DDRX) and particle-stimulated nucleation (PSN). Notably, EX-ECAP-induced grain boundaries (GBs) exceeding 30° significantly strengthen the alloy while modulating plastic deformation behavior. Ultimately, the synergistic effects of Mg 2 Pb, Al 3 Sc and Mg 17 Al 12 phases have optimized the strength-ductility of the multi-scale heterostructured MPAB-xSc alloy.