Unsteady-State Horizontal Solidification of an Al–Si–Cu–Fe Alloy: Relationship Between Thermal Parameters and Microstructure with Mechanical Properties/Fracture Feature

Abstract

Aluminum casting alloys have properties which are of great industrial interest, such as low density, good corrosion resistance, high thermal and electrical conductivities, good combination of mechanical properties, good workability in machining processes and mechanical forming. Currently, these alloys are produced in various systems and dozens of compositions. In this investigation, a mutual interaction of thermal parameters, scale of the dendritic microstructure, intermetallic compounds (IMCs), microhardness and tensile properties/fracture characteristics of a casting Al–7wt%Si–3wt%Cu–0.3wt%Fe alloy was analyzed. Solidification experiments were developed using a furnace that promoted horizontal growth under transient heat flow conditions. Then, growth rate (VL), cooling rate (CR), and local solidification time (tSL) were determined from measured temperature profiles. Secondary dendritic spacings (λ2), Si particles, Fe-rich and Al2Cu intermetallic phases were characterized by optical and SEM microscopy, as well as the area mapping and point-wise EDS microanalysis. Hence, the interrelations involving Vickers microhardness (HV), yield strength (σYS), ultimate tensile strength (σUTS) and elongation (E%) with microstructural features were evaluated by mathematical equations. IMCs as well as morphologies of Si were also analyzed in the fracture regions. In addition, the experimental growth law of λ2 = f(tSL) proposed in this study was compared with a predictive theoretical model reported in the literature for multicomponent alloys. It was observed that areas that tend to grow faster (lowest λ2 values) were associated with the highest σUTS and E% values, while HV and σYS properties were not affected by the thermal and microstructural parameters (CR and λ2). In addition, less extensive cleavage planes accompanied by small dimples in were observed in fractured samples with lower λ2 values.