Melt Cooling Rate Effect on the Microstrucutre of Al–Si Alloy Doped with Mg, Mn, Fe, Ni, and Cu

The microstructure, the grain structure, and the elemental composition of the Al–11.8Si–0.6Mg–0.4Mn–0.6Fe–0.8Ni–1.7Cu alloy (wt %) fabricated at melt cooling rates of 102 and 105 K/s have been investigated by scanning electron microscopy, electron backscattered diffraction, and electron-probe microanalysis. An increase in the cooling rate of the melt from 102 to 105 K/s refines the structural constituents of the alloy (grain sizes, intermetallic particle sizes, silicon particle sizes) by two orders of magnitude. The foil formed at a melt cooling rate of 105 K/s has a layered microstructure in the cross-section. High-rate solidification provides a constant concentration of elements in the layers. The formation of nanoinclusions in the foil layer adjacent to the mold has been explained. The composition of submicron (up to 200 nm) compounds localized at the boundaries of eutectic grains in the layer at the freely solidified side has been identified.