Achieving Superior Strength-Ductility Synergy in 5xxx Al Alloy Via Powder Forging-Rolling-annealing: Multi-scale Microstructure Evolution and Strengthening Mechanism

To address the critical demand for lightweight and high-strength materials for energy conservation and emission reduction, this study presents a novel composite process of “high-energy ball milling-powder forging-rolling-annealing” to fabricate a high-performance Al-5 Mg alloy. This route enables mechanical alloying and nanostructuring, producing a metastable microstructure characterized by a supersaturated solid solution, high-density dislocations, and stacking faults. Subsequent deformation and annealing result in a uniform ultrafine-grained structure with average grain sizes of 0.40 μm (forged) and 0.83 μm (rolled and annealed). A key finding is the phase transformation pathway regulated by the synergistic effect of intense deformation and mechanochemical reaction. Notably, no β-Al₃Mg₂ constituent particles are detected throughout the processing; instead, dispersed nano sized MgO particles are formed in situ. Multi scale characterization further confirms the presence of multiple defects, including high dislocation densities and dispersed nano MgO, which collectively contribute to an enhanced strengthening synergy. As a result, the alloy exhibits exceptional mechanical properties: tensile strengths of ∼692 MPa (forged) and ∼698 MPa (rolled and annealed) - far exceeding those of conventional Al-5 Mg alloys - while the rolled-annealed condition also provides improved ductility. This work demonstrates that microstructural and phase engineering via process innovation offers an efficient and industrially viable pathway for developing high strength AlMg alloys.