Microstructure and microhardness in horizontally solidified Al–7Si–0.15Fe–(3Cu;0.3Mg) alloys

Abstract

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 (G_R), cooling rates (C_R), 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.(G_R)^-1.1 and λ₃ = constant.(C_R)^-0.55 best describe the variation of λ₃ with corresponding thermal and microstructural parameters.