Breaking the trade-off between strength and ductility in an Al-Zn-Mg-Cu alloy enabled by high-density low angle grain boundaries and dual-scale nano-precipitates

Age-hardenable aluminum alloys typically exhibit a trade-off between strength and ductility, where precipitation strengthening inevitably leads to a loss of ductility. In this work, the strength-ductility trade-off is circumvented in an Al-6Zn-2Mg-1.5Cu-0.15Zr-0.2Sc alloy, where a high yield strength of ∼568 MPa and a favorable elongation of ∼15.9% are obtained. The strength-ductility synergy is benefited from a distinctive microstructure, featuring densely arranged low angle grain boundaries (LAGBs) and high-density dual-scale nano-precipitates. In particular, these nano-precipitates include both shearable GPII zones (average width of ∼1.9 nm), and non-shearable η′ (mean diameter of ∼4.6 nm) alongside Al 3 (Sc,Zr) (mean diameter of ∼10 nm). Such a tailored microstructure is achieved through a well-designed thermomechanical route integrating hot rolling, solid solution treatment and artificial aging. The high strength stems mainly from dual-scale precipitation strengthening, i.e., the relatively coarser Al 3 (Sc,Zr) and η′ precipitates contribute to Orowan strengthening, while the finer GPII zones provide shearing strengthening. Meanwhile, the high proportion of LAGBs accounts for significant grain boundary strengthening. The well-maintained ductility is attributed to dispersed nano-precipitates and densely distributed LAGBs, which jointly alleviate local stress accumulation, preserve dislocation motion capacity and meanwhile delay strain localization during plastic deformation. This study provides novel insights for developing age-hardening aluminum alloys with both high strength and ductility via synergistic regulating of LAGBs and nano-precipitates through an industry-applicable rolling route.