Effect of Sc on microstructural and mechanical behavior of Al–Cu–Mg alloy via wire-powder-arc additive manufacturing

In this study, thin-wall components of 2024 aluminum alloy modified with Sc addition were fabricated using the wire-powder arc additive manufacturing (WPAAM) method. Leveraging transient nucleation theory, we systematically analyzed the formation mechanism of fully equiaxed grain structures and quantitatively evaluated the strengthening mechanisms of Sc addition on mechanical properties in both as-deposited and T6 heat-treated states. Experimental results show Sc addition remarkably refines grains, transforming columnar to equiaxed structures and reducing average grain size from 78.0 to 12.3 μm. In the as-deposited state, this enhances yield strength, tensile strength, and elongation primarily via grain refinement. However, Sc addition also led to the formation of the W (Al_5.5Cu_6.5Sc) phase during solidification, reducing Cu content in the matrix. After T6 treatment, precipitation hardening was enhanced by the formation of refined S-phase precipitates. The addition of Sc reduced the volume fraction of the S phase as a result of Cu being consumed, while also restricting the growth of the S phase, thereby reducing its average size by 36.6 %. Consequently, the 2024Sc alloy achieved comparable T6 strength to the unmodified 2024 alloy while exhibiting a 47 % improvement in ductility.