Evolution of the Eutectic Microstructure in Chemically Modified and Unmodified Al-Si Alloys

Guthy, Hema Vardhan

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Evolution of the Eutectic Microstructure in Chemically Modified and Unmodified Al-Si Alloys

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Aluminum-silicon alloys are an important class of commercial non-ferrous alloys having wide ranging applications in the automotive and aerospace industries. Typical aluminum-silicon alloys have two major microstructural components, namely primary aluminum and an aluminum-silicon eutectic. While nucleation and growth of the primary aluminum in the form of dendrites have been well understood, the understanding of the evolution of the Al-Si eutectic is still incomplete. The microstructural changes caused by the addition of strontium to these alloys is another important phenomenon that still puzzles the scientific community. In this thesis, an effort has been made to understand the evolution of the Al-Si eutectic in the presence and absence of strontium through two sets of experiments: (1) Quench experiments, and (2) sessile drop experiments. The quench experiments were designed to freeze the evolution of the eutectic after various time intervals along the eutectic plateau. The sessile drop experiments were designed to study the role of surface energy in the formation of the eutectic in the presence and absence of strontium. Both experiments were conducted on high purity alloys. Using observations from these experiments, possible mechanis(s) for the evolution of the Al-Si eutectic and the effects of strontium on modifying the eutectic morphology are proposed.

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