Abstract: Gradient microstructural design offers a promising strategy to overcome the strength-ductility trade-off in metals with low stacking fault energy (SFE). However, its effectiveness in aluminum alloys is significantly constrained by two key factors: strain-induced precipitate dissolution and an insufficiency of deformation carriers (e.g., stacking faults or twins) due to inherently high SFE. Here, we demonstrate that ultrahigh strain rate deformation generates a gradient microstructure in a high-strength aluminum alloy. Crucially, this microstructure subsequently triggers a spontaneous nanoscale secondary precipitation process during ambient storage. This sequential process produces a synergistic effect, enhancing both the strength and ductility of the material beyond levels achievable via conventional heat treatments alone. The resulting gradient architecture, featuring a hard exterior and a soft core, contributes to improved strength while preserving superior resistance to mechanical damage. Concurrently, the nanoscale secondary precipitates effectively mitigate the detrimental precipitate-free zones typically formed during thermal aging, thereby suppressing localized plastic deformation and associated damage. These findings provide a viable pathway for optimizing the strength-toughness synergy in precipitation-strengthened alloys.

Key words: Gradient microstructures, Laser shock peening, Precipitation-free zones, Strength and ductility, High-strength aluminum alloys