Microstructural evolution and phase constituents of Al–Cu–Li alloys with different Mg and Zn contents during homogenization

The as-cast of Al-Cu-Li alloys generally necessitates a homogenization treatment to achieve a uniform microstructure, which effectively alleviate severe elemental segregation. However, during homogenization, the specific mechanisms by which micro-alloying elements influence the homogenization kinetics and the evolution of microstructural constituents remain insufficiently understood. In present paper, four Al-Cu-Li alloys with designed Mg/Zn contents were prepared. The microstructural characteristics and the evolution of microstructural constituents during homogenization were systematically characterized, using optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), electron probe micro - analysis (EPMA), differential scanning calorimetry (DSC), and the application of Scheil solidification modeling. The results demonstrate that Mg significantly retards the homogenization process by stabilizing high-melting-point intermetallic phases, such as Al 7 Cu 3 Mg 6 , and impeding solute diffusion. In contrast, Zn promotes the dissolution of non-equilibrium intermetallic phases and lowers the required homogenization temperature, primarily by facilitating the formation of low-melting-point Zn-containing phases (e.g., Al 2 Zn). When Mg and Zn are simultaneously added to the alloy, complex microalloyed intermetallic compounds such as Mg 32 (Al, Zn) 49 were formed. That leads to a non-monotonic dependence of homogenization difficulty on the Mg/Zn ratio, characterized by an initial decrease followed by an increase. The study systematically clarifies the opposing roles and interactive effects of Mg and Zn during the homogenization of Al-Cu-Li alloys, thereby providing a theoretical foundation for optimizing alloy composition and heat treatment parameters.