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).

The laminated LA141 sheets were processed by the accumulative roll bonding (ARB). The interaction between dislocations and laminated interfaces, and the effect of bond interface spacing on the dynamic recrystallisation (DRX) behavior and mechanical properties were investigated. The results show that, with the increase of ARB cycles, physical metallurgical bonding is enhanced. MgLi₂Al nanophases and fragmented MgO particles are formed at the bond interface during ARB process, which has a significant positive effect on the interface bonding. With the increase of ARB cycles, the bond interface spacing decreases, DRX mode changes from continuous dynamic recrystallization (CDRX) to geometrical dynamic recrystallization (GDRX), and the Zener-pinning effect is enhanced, which facilitates the grain refinement strengthening. The bond interface can not only effectively hinder the movement of dislocations causing strengthening, but also absorb, reflect and transmission the dislocations causing the improvement of the ductility. The final LA141 alloy possesses a tensile strength of 247 MPa and an elongation of 16.6 %, of which is 93.0 % and 70.3 % higher than the as-cast alloy, respectively.