Ce-Mediated Second-Phase-Reconstruction-Coupled Regulation of Mechanical–Corrosion Properties of As-Cast 8021 Aluminum Alloy Billet for Battery Foil

To optimize the overall performance of as-cast 8021 aluminum alloy billets for power battery foil, this study explores how Ce addition (0–0.4 wt.%) regulates microstructure, mechanical properties, and corrosion resistance via second-phase reconstruction. Microstructure characterization, mechanical property testing and electrochemical corrosion tests were performed. The results show that Ce addition first refines, then stabilizes, and finally coarsens α-Al grains. The addition of 0.2 wt.% Ce promotes the formation of tentatively identified dispersed Al–Ce–Fe ternary phases, achieving the optimal combination of ductility (elongation: 42.7%) and strength (tensile strength: 95.0 MPa), as well as superior corrosion resistance (icorr = 2.79 × 10−7 Acm−2). Excessive Ce led to possible precipitation of the Al2Ce phase and grain coarsening, deteriorating alloy properties. In conclusion, 0.2 wt.% Ce is the optimal content to balance the microstructure, mechanical and corrosion properties of 8021 aluminum alloy, providing a theoretical basis for its compositional optimization of as-cast billet for battery foil applications.