Synergistic improvement of strength and ductility in graphene nanoplatelets/Mg-14Li-1Al composites via heterogeneous phase regulation

• GNPs/LA141 composites with high strength and high plasticity are successfully fabricated by utilizing the accumulative roll bonding and friction stir processing. • The α-Mg/β-Li phase structure with a Burgers orientation relationship and the plate-like α-Mg phase were discovered for the first time in the LA141 alloy. • The interface structure between GNPs and the matrix is disclosed and the influence mechanism of this structure on the plasticity of materials is explored. • A multiscale heterogeneous synergistic strengthening mechanism was established, achieving a coordinated enhancement of both high strength and high ductility. This study innovatively proposed a synergistic processing strategy combining accumulative roll bonding (ARB) and friction stir processing (FSP), and successfully prepared graphene nanosheets/Mg-14Li-1Al (GNPs/LA141) composites with both high strength and high plasticity. The multi-scale heterogeneous synergistic strengthening mechanism of the composite material was systematically revealed. During the FSP process, GNPs stimulates dynamic recrystallization (DRX) and restricts grain growth, achieving significant grain refinement. An α-Mg/β-Li phase structure with Burgers orientation relationship was formed in the matrix, among which the plate-like α-Mg phase was first reported in the LA141 alloy. By optimizing the orientation distribution of GNPs through the rolling process, the GNPs/LA141 composite exhibits excellent mechanical properties: a yield strength of 237 MPa, a tensile strength of 259 MPa, an elongation of 12.1 % and a specific strength reaching 195 kN·m/kg. The α-Mg phase, in synergy with Al-rich precipitates, strengthens the composite through the Orowan mechanism, while micro–nano layered GNPs enhance its strength via the load transfer mechanism. Meanwhile, during the crack propagation process, the bridging and pull-out behavior of GNPs increases the energy required for fracture and effectively coordinates the synergistic improvement of strength and plasticity. This work provides an integrated control strategy of structure and performance for the design of multi-scale reinforced metal matrix composites (MMCs).