Unveiling Solidification Mechanism and Balanced Strength–Ductility Synergy of Eutectic High‐Entropy Alloys

ABSTRACT Eutectic high‐entropy alloys (EHEAs) have attracted significant attention due to their balanced mechanical properties and promising applications. Nonetheless, the correlation between the solidification mechanism of eutectic microstructures and their mechanical properties remains elusive. In this study, we report an Al 1.19 CoFeNi 2.86 EHEA composed of typical regular and irregular lamellar colonies. Both colonies exhibit a dual‐phase structure containing face‐centered cubic (FCC) and body‐centered cubic (BCC) phases, which collectively induce balanced as‐cast strength–ductility synergy. Tensile experiments reveal an as‐cast yield strength of ∼618 MPa, an ultimate tensile strength of ∼1015 MPa, and a fracture elongation of ∼9.7%. Through multiscale probing of deformation processes, we unveil that the mixed, regular and irregular, eutectic lamellar microstructure is critical for balancing strength and ductility, stemming from persistent hetero‐deformation‐induced strain hardening spanning across a wide strain scope. The hybrid structure of regular and irregular lamellar eutectics arises from solute diffusion and associated thermophysical factors during solidification. These findings provide insights into clarifying the structure–property correlation in as‐cast EHEAs as well as optimizing their properties.