Strength-ductility trade-off in high-Mg aluminum alloys via Y/Gd-induced heterogeneous microstructure

Abstract

When the Mg-content in 5-series aluminum alloys is ≥ 5 wt%, ductility significantly decreases despite a notable increase in strength. To address this issue, we added 0.18 wt% Y and 0.35 wt% Gd to Al-8.2Mg-0.5Mn alloys and investigated the alterations in their microstructure and properties after homogenization, hot/cold rolling, and annealing. This process introduces numerous fine Mn₂Gd phases (30–400 nm) uniformly distributed within the alloy, alongside a coarse Al₈Mn₄(Gd, Y) phase (1–50 μm). Both phases contribute to forming a heterogeneous grain structure, resulting in a high strength and ductility after a short-duration annealing period of 10 min at 430 °C (UTS ⁓479 MPa, EL⁓21.9 %). The excellent synergy between strength and ductility after short-duration annealing can be attributed to the high solute Mg content, the diffusely distributed fine second phase and grain refinement. In addition, its excellent ductility is also closely related to the high proportion of recrystallized grains (89.3 %) and the heterogeneous grain structure. This paper provides a feasible method to break the synergy between strength and ductility in high-magnesium aluminum alloys.