Abstract
Commercial AlSi7Mg alloy represents the usual choice for complex geometry casting production. The market imperative to improve mechanical properties imposed the design of new chemical composition of AlSi7MgCu alloy with high content of Cu (up to 1.435 wt.%). This represents a challenge in order to achieve advanced properties. The interaction of a number of alloying (Si, Mg, Cu) and trace elements (Fe, Mn) influenced a wide range of complex reactions occurring and therefore leading to intermetallic phase precipitation. The characterization of novel chemical composition interaction and its solidification sequence was achieved by modelling an equilibrium phase diagram, simultaneously performing both thermal analysis and metallographic investigations. Copper influence was indicated in the whole solidification process starting with infiltration in modified Chinese script phase Al15(Fe,Mn,Cu)3Si2, beside common intermetallic Al5FeSi. Copper addition encourages formation of compact complex intermetallic phases Al5Cu2Mg8Si6 and Al8(Fe,Mn,Cu)Mg3Si6. Solidification ended with secondary eutectic αAl + Al2Cu + βSi. Microstructure investigation allows volume reconstruction of the microstructure and distribution of particular phases. Chemical compositions enriched in copper content and developed microstructural constituent through solidification sequence of AlSi7MgCu alloy contribute to a significant increase in mechanical properties already in an as-cast state.
Highlights
High market demands related to material quality and properties strongly influence redesigning of common safety loaded aluminum alloy castings
The EDS investigation widened the palette of phases in which it occurs during the whole solidification process: Al15 (Fe,Mn,Cu)3 Si2 at the begging of the solidification after dendrite network development, in intermetallic phase Al5 Cu2 Mg8 Si6, Al8 Mg3 (Fe,Mn,Cu)Si, and Al7 Cu2 Mg developed after main eutectic reaction, and in a secondary eutectic Al + Al2 Cu + Si as a last solidifying phase
The investigation of redesigned innovative AlSi7MgCu alloy reveals the interaction of alloying and trace elements resulting in wide range of complex reactions and possible intermetallic phases responsible for tensile strength development
Summary
High market demands related to material quality and properties strongly influence redesigning of common safety loaded aluminum alloy castings. The redesigning of chemical composition of high-strength aluminum alloys becomes significant for safety critical structural components in automotive industry. According to new chemical composition thermodynamic modelling of the phase diagram in equilibrium and non-equilibrium, the influence of Cu encourages the number of intermetallic phase developments. Phases such as Al5 Cu2 Mg8 Si6 , Al7 Cu2 Mg, and Al2 Cu are found responsible for the increase in tensile strength in a number of other commercial alloys. Sophisticated FIB-SEM analysis performed on a determined volume allowed
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