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Influence of Cu on the microstructure development of AlSi7MgCu

Designing and characterisation of AlSi7MgCu alloy with extra addition of Cu (up to 1.435 wt.%) represents a challenge in order to achieve advanced mechanical properties already in as-cast state. Microstructural investigation of AlSi7MgCu alloy reveals a wide range of complex reactions and possible intermetallic phases due to the interaction of alloying and trace elements. An extra addition of Cu (up to 1, 435 wt.%) as a secondary alloying element initiates an additional interaction with transition elements Fe, Mn and secondary alloying element Mg. Evolution of microstructure and determination of solidification sequence enables detail overview of solidification path in both states, as-cast and heat-treated. Enrichment of solidification process with complex intermetallic phases reveals following constituents: dendrite network ; iron- based needle-like Al5SiFe and / or complex Chinese script formation Al15(Fe, Mn, Cu)3Si2 ; main eutectic (αAl+βSi) ; complex eutectic clusters of Al8Mg3(Fe, Mn, Cu)Si6 and Al5(Fe, Mn, Cu)2Mg8Si6 phase and secondary eutectic phase precipitations αAl+Mg2Si and αAl+Al2(Fe, Mn, Cu). Infiltration of common transition elements such as Fe and Mn in Cu bearing phases’ resulted in high total content of transition elements (Fe+Mn+Cu). Microstructural investigation also indicates continuous interaction of Fe, Mn and Cu in formation of wide range of intermetallic phases´ through the whole solidification process. The nature (morphology and alloying elements interaction) of formed intermetallic phases comprehends to the tensile mechanical properties development due to strong connections and interactions during solidification process as a whole.

AlSi7MgCu alloy, copper, microstructure, transition elements

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