The synergistic effect of ultrasound and Er on the microstructure and mechanical properties of an Al–Cu alloy with high Fe content

The large-sized needlelike iron-rich phases are detrimental to the grading utilization of the recycled Al alloys. In this paper, an effective method is put forward for the microstructural modification of an iron-containing Al–Cu alloy through simultaneously adding Er and applying ultrasound during solidification. The results show that coarse α-Al grains and a considerable amount of large-sized needlelike Al 3 Fe phase are observed in the sample neither adding Er nor applying ultrasound, while the size and continuity of acicular Al 3 Fe phase gradually decrease as the Er content increases. Meanwhile, α-Al grains are refined and a small portion of acicular Al 3 Fe phase transforms into platelike α-Fe phase with Er addition. Applying ultrasound alone, α-Al grains are refined by 21.1 % and the average length of needlelike Al 3 Fe phase is reduced by 33.5 % in comparison with the conventional sample. In contrast, synergistically applying ultrasound and adding 0.3 % Er significantly promotes the large-sized needlelike Al 3 Fe phase to transform into small-sized lamellate α-Fe phase, with grain refinement of 40.8 % and a 60.9 % reduction in the average length of needlelike Al 3 Fe phase. This is primarily ascribed to that cavitation and acoustic streaming facilitate the formation of dispersive Er-rich phases, which impedes the growth of coarsening needlelike Al 3 Fe phase and provides more sites as well as interface conditions beneficial to the nucleation of α-Fe phase. Correspondingly, the mechanical properties of the alloy sample with ultrasound and 0.3 % Er addition exhibit a substantial improvement in comparison to the conventional sample.