Rapid solidification of undercooled Al-Cu-Si eutectic alloys

Under the conventional solidification condition, a liquid aluminium alloy can be hardly undercooled because of oxidation. In this work, rapid solidification of an undercooled liquid Al(80.4)Cu(13.6)Si(6) ternary eutectic alloy was realized by the glass fluxing method combined with recycled superheating. The relationship between superheating and undercooling was investigated at a certain cooling rate of the alloy melt. The maximum undercooling is 147 K (0.18T(E)). The undercooled ternary eutectic is composed of alpha(Al) solid solution, (Si) semiconductor and theta(CuAl(2)) intermetallic compound. In the (Al+Si+theta) ternary eutectic, (Si) faceted phase grows independently, while (Al) and theta non-faceted phases grow cooperatively in the lamellar mode. When undercooling is small, only (Al) solid solution forms as the leading phase. Once undercooling exceeds 73 K, (Si) phase nucleates firstly and grows as the primary phase. The alloy microstructure consists of primary (Al) dendrite, (Al+theta) pseudobinary eutectic and (Al+Si+theta) ternary eutectic at small undercooling, while at large undercooling primary (Si) block, (Al+theta) pseudobinary eutectic and (Al+Si+theta) ternary eutectic coexist. As undercooling increases, the volume fraction of primary (Al) dendrite decreases and that of primary (Si) block increases.