Influence of silicon and magnesium on grain refinement in aluminium alloys

Abstract

Grain refinement in Al-Si alloys with silicon contents in the range of 0.2-30 wt-% has been studied in detail with conventional as well as higher level additions of a Al-5Ti-1B master alloy. A poisoning effect was observed with Al-Si alloys containing ≥7 wt-%Si and the extent of poisoning increased with an increase in the silicon content. Silicon improves the grain refining behaviour of aluminium when added in small quantities (0.2%). Magnesium can counteract the poisoning effect of silicon. The optimum level of magnesium required to overcome the poisoning effect depends on the silicon content of the alloy. Higher level additions of a grain refiner could overcome the poisoning effect of silicon and the level required to achieve good grain refinement is a function of the silicon and magnesium contents of the alloy. The present paper also reports the influence of degasser and melt