Modification of the microstructure of hypoeutectic Al-Si alloys

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The aim of the project was and is to clarify the effect of strontium on the formation of the eutectic microstructure of hypoeutectic (xSi<12%) Al-Si alloys. Although the beneficial action of up to 200 ppm strontium has been known at least since 1922 the mechanism of its action is still unknown. Therefore the emphasis of the current work is to identify where strontium is segregated during solidification, how it influences the structure of the eutectic silicon and which mechanism is responsible for the effect. Moreover the influence of important alloying elements and impurities such as Fe, Mn and P and their interaction with strontium has to be studied. Especially the formation of intermetallic phases and its dependence on the presence of Sr is of practical (mechanical properties) and fundamental interest.