The role of transition metal additions on the ambient and elevated temperature properties of Al-Si alloys

The principal aim of the present study was to investigate the effects of small additions of several transition metals (Zr, Ni, Ti, IT, Cr, La, Y and Nb) on the microstructure, tensile properties and failure mechanisms of as cast Al-10Si alloys at ambient and elevated temperatures (200 and 250 degrees C). Transition metal addition led to the formation of (AlSi)(3)(TiZr), (AlSi)(3)(CrVTi), Al-13(FeCrVTi)(4)Si-4, (AlSi)(3)(CrV), Al9FeNi, AlNbTiZr, AlSiV, AlSiYLa and AlSiZrTiNb phases which are thermally stable until incipient melting of the eutectic compound occurs. Addition of Zr, Ni, Ti, V and Cr gave a substantial improvement in tensile strength at 250 degrees C, but at the expense of reduced ductility. The strength of transition metals-containing alloys is strongly governed by the size and morphology rather than the volume fraction of the intermetallic phases formed. Large and irregular particles such as (AlSi)(3)(TiZr), (AlSi)(3)(CrVTi), AlNbTiZr and AlSiV provided inhomogeneity in the alpha-Al matrix and act as the principal source of stress concentration, playing an active role in crack initiation. Crack propagation was primarily controlled by plastic deformation of high cooling rate-refined dendrites and modified eutectic silicon particles.