Modification of Al-Si Microstructure - The Al-Si-Sr Phase Diagram from 0–20 WT. % Si and 0–5.0 WT. % Sr

ABSTRACTIt is well known that the morphology of primary and eutectic silicon resulting from solidification is sensitive to minor impurity additions: “modification” by alkali and alkaline earth metals is common foundry practice and the use of strontium is of recent and current interest because its effect is retained in liquid metal for relatively long times. The mechanism for modification remains obscure and is not necessarily the same from one elemental addition to the next, but it is essential to separate the equilibrium and kinetic influences if the phenomenon is to be better understood. Accordingly, the liquidus surface and eutectic reactions have been located in the relevant part of the Al-Si-Sr system by careful thermal analysis and the results correlated with the microstructure. Comparison is made with the parallel behavior of alkali metal additions.