Tailoring microstructural heterogeneity in sandwich-structured pure Al laminates for enhanced strength-ductility synergy

In this study, a novel design strategy was developed to overcome the strength-ductility trade-off in pure aluminum (Al) by constructing sandwich-structured laminates with pronounced microstructural heterogeneity. An accumulative roll bonding (ARB) process was employed to produce an ultrafine-grained (UFG) intermediate layer, which was sandwiched between two fully recrystallized coarse-grained (CG) pure Al outer layers via cold rolling. The produced laminate was then annealed at 300 °C for varying durations to regulate the microstructure. Tensile tests revealed that the laminate annealed for 30 min achieved a superior strength-ductility balance, exhibiting a yield strength of 106 MPa alongside a uniform elongation of 11.3%. Microstructural characterization confirmed pronounced microstructural heterogeneity across the hetero-interfaces. In-situ digital image correlation (DIC) and in-situ tensile observations demonstrated significant strain gradients at these interfaces, which necessitated the accumulation of geometrically necessary dislocations (GNDs) for accommodation. This mechanism generated hetero-deformation induced (HDI) strengthening and HDI strain hardening, thereby enhancing both strength and ductility. This work elucidates the coordinated deformation behavior between soft and hard domains in sandwich-structured pure Al laminates and demonstrates an effective strategy for achieving high performance in pure Al via architectural heterogeneity.