Influence of Sc addition and rapid solidification on the microstructure and mechanical properties of Al-5Cu alloys

Abstract In this study, Al-5Cu-based alloys were doped with 0.5 wt% and 1 wt% scandium (Sc), and the resulting compositions were processed into melt-spun ribbons under high cooling rates to examine their mechanical and microstructural properties. The chemical compositions of the alloys were confirmed by XRF analysis, and XRD analysis showed the presence of α-Al and θ-Al 2 Cu phases, while Sc-containing alloys additionally showed low-intensity peaks attributed to the finely dispersed Al 3 Sc phase. In the melt-spun ribbons, the XRD patterns exhibited significant peak broadening and merging, suggesting the formation of metastable intermetallic compounds and possible ternary phases such as Al 4 Cu 9 Sc or AlCuSc 2 in Sc-rich and Cu-rich regions. SEM-EDX analyses demonstrated that rapid solidification resulted in much finer grain structures, although a slight coarsening of intermetallics was observed with increasing Sc content. Mechanical testing revealed improved hardness and elastic modulus with Sc addition, yet a trade-off was noted in ductility, which decreased at higher Sc levels due to grain boundary precipitation. Overall, Sc additions improved the mechanical performance of rapidly solidified Al-5Cu alloys by refining the microstructure and promoting the formation of strengthening intermetallics. Still, excessive Sc led to the formation of coarser or more complex phases that slightly reduced ductility.