Effect of minor Sc and Fe co-addition on the microstructure and mechanical properties of Al-Cu alloys during homogenization treatment

Microstructures and mechanical properties of homogenized Al-2.5 wt% Cu (Al-Cu), Al-2.5 wt%Cu-0.3 wt%Sc (Al-Cu-Sc) and Al-2.5 wt%Cu-0.3 wt%Sc-0.2 wt% Fe (Al-Cu-Sc-Fe) alloys were comprehensively studied, which allowed to demonstrate the single Sc effect as well as the combined Sc and Fe effect on microstructural evolution during homogenization treatment and hence on mechanical response, respectively. It was clearly revealed that the single minor Sc addition refined the grains of as-cast Al-Cu alloy, and induced Sc enrichment in the micro-sized α-Al/θ-Al₂Cu eutectic. During homogenization, the Sc distribution highly affected the formation of micron-sized (Cu,Sc)-rich W-phases and submicro/nano-sized Al₃Sc dispersoids. In comparison, the co-addition of minor Fe and Sc produced grains and micro Sc-segregation similar to the single Sc addition. However, the formation of W phase was highly suppressed. This resulted in promoted Al₃Sc dispersoid formation during homogenization and led to improved strength. Unfortunately, coarse (Cu, Fe)-rich constituents were newly created in the homogenized Al-Cu-Sc-Fe alloy, and the ductility of alloy was correspondingly reduced.