Effect of Sc additions on precipitation behavior and creep- and coarsening resistance of a cast Al-4.5Cu-0.3Mg-0.4Ag (wt%) alloy

Abstract

The effects of solidification rates and solutionizing temperatures on V-phase (Al₈Cu₄Sc) nanoprecipitate formation and subsequent mechanical properties in a cast Al-4.5Cu-0.3Mg-0.4Ag-0.3Sc (wt%) alloy are evaluated. After solutionizing, Ω-Al₂Cu precipitates are formed upon aging at 185 °C and then transformed into Al₈Cu₄Sc V-phase precipitates at 400 °C, showing high coarsening resistance. Avoiding Al_8-xCu_4+xSc W-phase precipitation during solidification is crucial, as this phase reduces the concentration of Cu and Sc available in the matrix for Al₂Cu Ω-precipitation at 185 °C and the subsequent final formation of V-precipitates at 400 °C, affecting microhardness at ambient temperature and creep strength at 400 °C. Solutionizing temperatures between 580 and 600 °C dissolve the undesirable W-phase but form large stable θ-Al₂Cu phases, which also scavenge Cu. Furthermore, the W-phase was observed both under relatively fast solidification in a graphite mold and very slow solidification in a furnace, and the microhardness was similar under the two casting conditions. Similarly, adding 0.15Si wt% does not impact the mechanical properties of the alloy. These findings suggest that Al-Cu alloys with V-phase precipitates have promising potential for high-temperature applications, although further study of the processing techniques is necessary to fully utilize their capabilities.