Abstract: Studies on die-casting Al-based entropy alloys are very limited, and an in-depth understanding of their microstructure heterogeneity and aging behavior is vital for improving their performance and thus promoting their industrial applications. In this study, the microstructure heterogeneity and aging behavior of the die-casting Al₈₀Si₈Mg₄Cu₄Zn₄ alloy were investigated. The underlying formation mechanism was revealed. Results show that the surface experienced rapid cooling would lead to the formation of fine, randomly oriented grains. In contrast, the central region of the specimens exhibits pronounced crystallographic texture as a result of thermal gradients and solute movement. Rapid surface cooling boosts nucleation rates and restricts dendritic growth. Solute-rich segregation bands favor coarse, highly curved dendritic phases, whereas the center's slower solidification yields fewer, larger blocky structures with low curvature. Different externally solidified crystals (ESCs) distributions and cooling velocities lead to microstructure heterogeneity. The segregation band's reduced effective partition coefficient of segregation bands implies higher solute retention in the liquid phase, which indicates a strong segregation propensity. Artificial aging resulted in more significant hardening in the surface layer compared with that of the center, which is attributable to the faster precipitation rates and the formation of finer precipitates near the surface. Additionally, mechanical properties varied through the radius of the die-casting due to its heterogeneous microstructure. The presence of dense precipitates within the surface layer contributes to a surface hardening effect, which plays a role in strengthening the alloy through nonhomogeneous plastic deformation. The central region shows the weakest performance, which would be due to the limited solute solubility and coarse ESCs.

Key words: Die-casting, Al-based entropy alloys, Microstructure heterogeneity, Aging behavior, Mechanical properties