Revolutionizing coherent brittle δ′-Al₃Li precipitates by rapid amorphization in a multicomponent Al-Li-Cu alloy during two-step aging

Traditionally, it is believed that more nanometer precipitates would produce higher mechanical properties in heat treatable Al alloys. In this study, it has been found that the reduction of coherent δ′ nano precipitates in Al-Li and formation of heterogeneous amorphous-crystalline interfaces upon two step aging actually break the strength-plasticity trade-off in high-Li content Al-Li alloys by using In-situ small-angle neutron scattering (SANS). By suppressing δ′ over-precipitation while inducing dynamic dissolution-reprecipitation cycles, excessive brittle δ′ (Al₃Li) precipitates have been dissolved by an effective short-term two-step aging protocol (120 °C/4 h + 175 °C/20 min). SANS quantification of the temperature-dependent δ′ precipitation kinetics clearly demonstrates a dissolution-dominated regime at 175 °C that destabilizes classical coarsening models. Crucially, transient amorphization triggered by Li segregation forms heterogeneous amorphous-crystalline interfaces, which enhances plasticity and strain hardening by more effectively impeding dislocation shearing. These findings establish a new microstructure-tailoring strategy where controlled δ′ dissolution and meta-stable amorphization synergistically bypass strength-ductility compromises in Al-Li alloys.