The Mg-8Gd-3Er-0.5Ag-0.5Zr (wt.%) alloy fabricated by hot-extrusion + stamping exhibits an exceptional aging hardening response, with the yield strength being improved by >200 MPa. Traditional extrusion microstructure was observed in the as-extruded sample, with the elongated non-recrystallized grains showing typical (1010) fiber texture. After stamping, almost all non-recrystallized grains were twinned mainly following the (1012) twin orientation. This significantly changed precipitate morphologies formed during the following aging, from the well-known granular β′ precipitate into net-work β′ + β′_H structure, with the granular β′ precipitates being connected by chain-like β′_H precipitates. Additionally, a novel fault was found in the β′ precipitates, whose formation is highly related to the metastable I₂-type stacking fault. This new precipitation structure means the effective interparticle spacing being approximately zero, and the faults in the β′ precipitates can not only enhance strength of precipitates but also could efficiently impede dislocation motion, thus resulted in positive contribution on alloy’s yield strength. This work provides new insights in developing high-strength Mg alloys by modifying precipitation structure along with the inner faults in precipitation.

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.

Mg-Li alloys with high lithium concentrations possess a lightweight body-centered cubic (BCC) matrix structure (β-Li). Interspersed eutectics (primarily the reticulated I-phase) often form along phase boundaries (PBs) and grain boundaries (GBs) which strengthen the alloy but cause the loss of ductility due to the brittle behavior of I-phase. By modifying the Li content, we fabricated the (β+α) biphase Mg-Li alloy in which the α-Mg phase with a hexagonal close-packed structure (HCP) is embedded in β-Li matrix, significantly increasing interface density. The high-density interfaces mitigate the distribution and dimension of the I-phase along GBs and PBs. The alloy exhibits enhanced ductility (elongation (EL) = 17.8 %) compared with the alloy without the α-Mg phase (EL = 5.1 %). Structural characterizations unveil the strengthening mechanism of the nanoscale B2 (Li, Mg)₃Zn-type precipitates in conjunction with the microscale I-phase. The (Li, Mg)₃Zn nanophases augment the yield and ultimate tensile strength of the alloy without a discernible compromise in ductility, predominantly due to gliding dislocations cutting through the precipitates. In contrast, the microscale I-phase presents a formidable barrier to dislocation motion, facilitating dislocation pileups at interfaces and culminating in diminished ductility across the interface. In-situ stretching techniques were employed to scrutinize the microstructural evolution of alloys during tensile deformation, elucidating that the deformation compatibility of alloys correlates with the average size of the I-phase and their distribution along GBs and PBs. Corresponding to the orientation relationship (OR) between the α-Mg and β-Li phases {110}Li//{0001}Mg and <111>Li //<1120>Mg, the slip continuity between α-Mg and β-Li on plane pairs of {123}Li-{1122}Mg and {112}Li-{1122}Mg assures the deformation compatibility through facilitating the deformation across interfaces. Simultaneously, during the stretching process, the dispersed I-phase instigates the emergence of sporadic microcracks, indicating gradual damage evolution. These discoveries offer novel insights into achieving exceptional strength-ductility amalgamations in Mg-Li alloys through microstructural adjustments.