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An experimental study with an A356-AlSiMgFe alloy was developed to evaluate the microhardness performance in the microstructure resulting of an unsteady-state horizontal solidification process. The Al-7wt%Si-0.3wt%Mg-0.15wt%Fe alloy was elaborated and directionally solidified in a water-cooled horizontal solidification device. In order to experimentally determine the cooling and growth rates (V L and T R , respectively), a thermal analysis was also conducted during solidification. Microstructural characterization by optical microscopy, SEM/EDS elemental mapping and microanalysis of the punctual EDS compositions allowed to observe the presence of an Al-rich dendritic phase (Al (α)) with interdendritic phases second composed of an eutectic mixture: Al (α-eutectic) + Si + Al 8 Mg 3 FeSi 6(π) + Mg 2 Si (θ). Furthermore, the dendritic microstructure was characterized by measuring the secondary dendritic spacings (λ 2) along the horizontally solidified ingot. Higher HV values were observed within the eutectic mixture.

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Transient horizontal directional solidification (THDS) experiments have been carried out with Al–7wt.%Si–0.15Fe, Al–7wt.%Si–3wt.%Cu–0.15wt.%Fe and Al–7wt.%Si–0.3wt.%Mg–0.15wt.%Fe alloys, to identify experimental relationships between growth rates ( GR), cooling rates ( CR), tertiary dendrite arm spacings (λ3) and microhardness (HV). Optical microscopy and scanning electron microscopy/energy-dispersive spectrometry (SEM/EDS) were used to perform a comprehensive microstructural characterisation of the β-Al5FeSi, ω-Al7Cu2Fe, θ-Al2Cu, π-Al8Mg3FeSi6 and α-Mg2Si intermetallic phases. The addition of Cu and Mg to the Al–7wt.%Si–0.15wt.%Fe alloy led to the precipitation of ω and π phases from the β phase. It has been found for all analysed alloys that power experimental functions given by λ3 = constant.( GR)-1.1 and λ3 = constant.( CR)-0.55 best describe the variation of λ3 with corresponding thermal and microstructural parameters.