Tuning Internal Stress in Metals with Bimodal Particles for Exceptional Strength and Ductility

Microstructural heterogeneity and associated nonuniform internal stress in metallic materials are crucial for achieving excellent mechanical properties. However, general methods for controlling such heterogeneity remain scarce. Metal matrix composites are intrinsically heterogeneous materials with tunable microstructures. Here, we developed a micron/nano-bimodal reinforcement structure that optimizes internal stress distribution, which not only reduces local stress concentration at interfaces but also facilitates the extensive activation of nonpreferential slip systems in alloys. As a result, the representative Al2024 alloy exhibits an extraordinary true tensile strength of ∼750 MPa and impressive ductility (with elongation-to-failure exceeding 10%). Stress delocalization at interfaces and strong local dislocation interactions are synchronously prompted through internal stress tuning at the nanoscale, with the optimized size of fine particles being ∼1/10 of coarse reinforcing particles, contributing to sustained dislocation accumulation and, consequently, large tensile ductility.