Influence of silicon and magnesium on grain refinement in aluminium alloys

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 leve l additions of a Al-5 Ti-1 B master alloy. A poisoning effect was observed with Al-Si alloys containing greater than or equal to 7 wt-%Si and the exte nt of poisoning increased with an increase in the silicon content. Silicon improves the grain refining behaviour of aluminium when added in small quan tities (0.2%). Magnesium can counteract the poisoning effect of silicon. Th e optimum level of magnesium required to overcome the poisoning effect depe nds on the silicon content of the alloy. Higher level additions of a grain refiner could overcome the poisoning effect of silicon and the level requir ed to achieve goad grain refinement is a function of the silicon and magnes ium contents of the alloy. The present paper also reports the influence of degasser and melt temperature on the grain refining response of Al-Si alloy s. MST/4231.