The influence of pseudosurfaces on solidification of aluminum-alloys

Solidfication of bulk liquids in practice takes place with minimal supercooling suggesting the presence of solid-like surfaces in the melt. The paper describes the work carried out at the National Metallurgical Laboratory on the structure of liquid metals which has already indicated
that regions of denser atomic packing (clusters) than that in true liquid, exist in metallic melts. The recent develo-pments in the concept of these clusters acting as nuclea-ting substrates in place of the conventional crystallite nucleation theories has also been described. This concept
of nucleation by dusters has been proposed after discuss-ing the discrepancies of the crystallite nucleation mech-anisms particularly with reference to grain refining mechanism in aluminium alloy solidification.

The paper also briefly discusses various theories of grain refinement in aluminium and the newer developments in the grain refining practices that have taken place as a result of better understanding of the structure in the liquid state. The effects of melt superheat, mould temperature and quantity of inoculant on the grain refining efficiency has been enumerated.