Enhancing the strength and plasticity of laminated aluminum alloy by introducing micron-scale pure aluminum interlayers

Abstract

Laminated aluminum alloys (LAAs) are recognized as pivotal materials in aerospace and automotive structures, due to their low density and high specific strength. However, there is an inverse relationship between the strength and plasticity of these alloys, which restricts their further applications in a low-carbon economy. This study proposes the design of micron-scale pure Al interlayers between AA2024/AA7075 layers to inversely strengthen the LAAs by achieving collaborative deformation through interlayer stress gradients and dislocation path modulation, enabling simultaneous enhancement of strength and plasticity. Notably, the micron-layered Al composite (MLAC) exhibits an ultimate tensile strength of 503.4 MPa and elongation of 13.3 %, which are 18.6 % and 29.1 % higher than those of the traditional layered composites (TLACs), significantly surpassing the limitation of the mechanical properties of laminated materials obeying the rule of mixtures (ROM). The underlying strengthening–ductilizing mechanisms are unveiled by in-situ electron backscatter diffraction (EBSD), digital image correlation (DIC), crystal plasticity (CP), and molecular dynamics (MD) based simulations. Results reveal that the strength mismatch between the pure Al layer and the Al alloy layers induces progressive accumulation of soft-layer stress gradient, forming an interfacial stress-affected zone (ISAZs). These zones trigger intricate dislocation-grain interactions and evolve into networked strain bands through the coordinated activation of slip systems. By redistributing local stress fields, these strain bands promote plastic flow as the dominant stress dissipation pathway, dynamically balance interfacial stress concentrations, and induce subcritical microcrack formation, thereby suppressing the tendency for catastrophic brittle fractures. Consequently, these findings establish heterostructure-enabled interlayer design as an effective pathway to achieve strength–ductility synergy in AA2024/AA7075 laminates. The unveiled strengthening–ductilizing mechanism offers a conceptual framework for developing LAAs that transcend conventional mechanical property limitations, obeying ROM.