Effect of Sc Addition on the Microstructure and Mechanical Properties of Wire-Arc Directed Energy Deposition Al–Cu Alloys

The refined microstructure and enhanced mechanical properties of wire-arc directed energy deposition (WA-DED) Al-Cu alloys have attracted a great deal of attention in various industries. Despite numerous strengthening strategies developed to enhance the performance of Al-Cu alloys, the effect of scandium (Sc) in their as-deposited state has received limited attention. In this work, Al-Cu-Sc alloy samples with different Sc contents were designed and prepared by WA-DED technology with interlayer powder coating. The microstructural characteristics and mechanical properties of Al-Cu alloys with varying Sc contents were systematically compared by applying an alcohol-based solution with different Sc concentrations. The experimental results demonstrate that the addition of Sc promotes the columnar-to-equiaxed transition (CET). Moreover, compared to the Al-Cu-Sc alloy with lower Sc content (0.15%, average grain size: 128.35 μm), the alloy with higher Sc content (0.32%) exhibited a finer average grain size of 95.81 μm. The increased Sc content was also beneficial in suppressing the formation of solidification shrinkage pores. As the Sc content increases, the interconnected θ′-Al2Cu phase breaks up, leading to its more uniform dispersion in the aluminum matrix. In terms of mechanical properties, the sample with higher Sc content demonstrated superior tensile properties, exhibiting an ultimate tensile strength (UTS) and elongation (EL) of 265.89 MPa and 12.29%, respectively, compared to 240.67 MPa and 9.05% for the Sc-L sample. In contrast, the yield strength (YS) and microhardness showed no significant variation with the change in Sc content.