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Thermodynamic and microstructural characterization of AlSi8Cu3 alloy

The design of materials through the selection of the chemical composition, thermodynamic modelling, melt treatment by inoculation and modification, annealing and correctly developed casting technology could improve castings properties. Due to castings complex geometry, it is sometimes necessary to provide heat treatment such as annealing after casting. Rigorous regime with a relatively high temperature and long holding time indicates the microstructural changes in the material, thus indirectly affects the mechanical properties of the material. An important aspect for further improvement and application is to develop a better understanding of the microstructural constituent changes due to provided heat treatment. Hypoeutectic aluminum - silicon casting alloy such as AlSi8Cu3 (EN AC 46200) has found a wide commercial applications in automotive industry for safety components. Thermodynamical modelling enables an insight in solidification sequence of the AlSi8Cu3 alloy. Simultaneous thermal analysis reveals corresponding temperatures of phase transformations with predicted reaction on the base of thermodynamical modelling. The number and values of obtained phase transformations indicate homogenization impact of heat treatment, as confirmed by microstructural analysis. Investigation of microstructural features defines distribution, morphology and ratio of particular intermetallic compounds corresponded to heat treatment state. The aim of this work was to determine solidification sequence using thermodynamic modeling and establishment of heat treatment effect on the microstructure and mechanical features of separately cast test AlSi8Cu3 alloy samples. Metalographic analysis established following microstructural constituents: αAl primary dendrites, eutectic (αAl +βSi) and intermetallic phases based on copper stoichiometry Al-AlxCu-Si, AlxMgySizCuw. Annealed microstructure has been changed as more uniformly distribution of primary aluminum dendrites, its copper enrichment, and therefore fragmentation of the last solidifying phases based on copper.

Al-Si alloys ; thermodynamic modeling ; simultaneous thermall analysis ; microstructure ; heat treatment

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