Effect of eutectic Si particles on the defect susceptibility of tensile properties to microporosity variation in Al-xSi binary alloys

Abstract

The variability in the defect susceptibility of tensile properties to microporosity variation in as-cast Al-xSi binary alloys was investigated in terms of the effective void area fraction, which includes the area fraction and size distribution of micro-voids and eutectic Si particles. The test samples were prepared in the form of Al-xSi (x=2,5,8,11) alloys with 0.02wt%Sr modification using gravity-casting process. The tensile properties of Al-xSi alloys fundamentally depend on microstructural changes, with a remarkable deviation caused by microporosity variation. The defect susceptibility of the ultimate tensile strength and elongation is practically varied with the nominal area fraction of eutectic Si colonies, rather than the real fraction of eutectic Si particles. The damage evolution of Si particles practically influences the tensile properties of Al-xSi alloys, together with the variation of the area fraction of pre-existing micro-voids. Additionally, the relative contributions of microporosity and eutectic Si colonies to the variability in the defect susceptibility of tensile properties to an effective void area fraction can be definitively described by considering the incoherency parameter and the plastic constraint factor of both micro-components and by using a modified constitutive model. The tensile properties of Al-xSi alloy in the high fraction of eutectic Si colonies are practically degraded by the increase of microporosity, even though the tensile properties in the low fraction of eutectic Si colonies are insensitive to the microporosity variation.