Effect of Cu content on microstructural evolution and mechanical behavior of Al–Cu–Mg–Ag alloys

This study systematically investigates the effect of Cu content (2.77–6.80 wt%) on the microstructural evolution and mechanical behavior of Al–Cu–Mg–Ag alloys through comprehensive characterization using scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The relationship between microstructure and yield strength (YS) was quantitatively analyzed using multiple strengthening models. Experimental results demonstrate that increasing Cu content promotes eutectic phase formation (θ-Al 2 Cu, T-Al 20 Cu 2 Mn 3 and Ag-containing S-Al 2 CuMg) in as-cast microstructures, accompanied by a transition from dendritic to cellular dendritic grain morphology. Coarse surplus phases (CSPPs) facilitate particle-stimulated nucleation (PSN), enhancing recrystallization to a maximum of 88.91 % at 6.80 wt% Cu. The number density of the Ω phase exhibits a non-monotonic dependence on Cu content, reaching a maximum of 6.72E+22 m −2 at 4.68 wt% Cu, while θ′ phase precipitation is significantly suppressed. Mechanical properties and grain boundary characteristics show strong Cu content dependence: increasing Cu content reduces precipitate-free zone (PFZ) width and transforms grain boundary precipitates (GBPs) from discontinuous to continuous distributions. Yield strength demonstrates a positive correlation with Cu content, while ductility follows an inverse trend. Strengthening mechanism analysis reveals that Ω phase precipitation dominates the yield strength enhancement.