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

摘要

The principal aim of the present study was to investigate the effects of small additions of several transition metals (Zr, Ni, Ti, V, Cr, La, Y and Nb) on the microstructure, tensile properties and failure mechanisms of as-cast Al-lOSi alloys at ambient and elevated temperatures (200 and 250 ℃). Transition metal addition led to the formation of (AlSi)_3(TiZr), (AlSi)_3(CrVTi), Al_(13)(FeCrVTi)_4Si_4, (AlSi)_3(CrV), Al_9FeNi, 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 ℃, 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 α-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.