Modulated precipitation of dispersoids and strength-ductility synergy via multi-step pre-treatments in an Al-Mg-Mn-Fe-Zr-Cr-Si alloy

Conventional 5xxx Al-Mg alloys are typically non-heat-treatable, with their strength limited by solid solution and work hardening. Dispersion strengthening is a potent strategy to overcome this limitation, but its effectiveness is often hindered by the sluggish and insufficient precipitation of thermally stable dispersoids. To promote dispersion kinetics, this work introduced a multi-step pre-treatment, integrating pre-aging (PA, 300 °C/8 h) and pre-straining (PS, 10 % cold rolling), in a novel Al-Mg-Mn-Fe-Zr-Cr-Si alloy. This PA + PS protocol constructed a unique composite microstructure, featuring Mn-rich solute clusters, β-Mg₂Si nanoparticles and a high density of dislocations. Upon subsequent aging at 400 °C, the dislocation networks strongly interacted with β-Mg₂Si to cooperatively facilitate the heterogeneous nucleation of Mn-rich dispersoids, while the residual Mn-rich solute clusters in Al-matrix progressively transformed into dispersoids. This dual precipitation pathway effectively accelerated the aging kinetics and enhanced the spatial uniformity of dispersoids, thus drastically minimizing dispersoid-free zones (DFZs). Consequently, samples subjected to PA + PS exhibited a superior strength-ductility synergy after aging at 400 °C for 12 h, with yield strength, ultimate strength and elongation increased by 34 %, 40 % and 23 % over the as-cast counterpart. Furthermore, it demonstrated exceptional thermal stability, with negligible loss of strength even after prolonged 400 °C aging until 200 h, overwhelming the PS pre-treated and as-cast samples. This work establishes a transformative dispersion-strengthening paradigm mediated by the synergy of pre-aging and pre-straining, providing foundational insights for developing advanced, thermally stable 5xxx alloys with high strength-ductility synergy.