This study aims to evaluate the relative contribution of shrinkage voids and oxide bifilms to the tensile properties of Al-7Si-0.4Mg alloys in terms of defect susceptibility due to the existence of casting defects. Tensile specimens were fabricated via gravity casting using commercial A356 aluminum alloy, and the area fraction of casting defects was measured using scanning electron microscope (SEM) fractographic analysis of the tensile fracture surfaces. Shrinkage voids and oxide bifilms are representative casting defects that significantly influence the tensile properties of A356 alloys. When oxide bifilms are present alongside shrinkage voids, tensile properties exhibit greater sensitivity to changes in the area fraction of casting defects compared to specimens containing only micro-voids in the form of shrinkage voids containing a thin oxide film. However, the defect susceptibility coefficients for tensile strength and elongation under T6-treated conditions are somewhat lower than those observed in the as-cast specimens. In this study, the area fraction of oxide bifilms on the fracture surfaces of the tensile specimens averaged 12.5%, with an inclusion frequency of approximately 45%, which is relatively lower than that of shrinkage voids present on all fracture surfaces. The defect susceptibility coefficients for tensile strength and elongation in as-cast specimens where the casting defects consisted solely of oxide bifilms were approximately 3.58 and 11.34, respectively. These values represent clear increases of approximately 3.2 and 9.1 compared to specimens containing only shrinkage voids; a similar trend was observed under T6-treated conditions.
Citation: Choongdo Lee. Relative contribution of oxide bifilms and micro-voids to tensile property of Al-7Si-0.4Mg alloys[J]. AIMS Materials Science, 2026, 13(2): 282-299. doi: 10.3934/matersci.2026016
This study aims to evaluate the relative contribution of shrinkage voids and oxide bifilms to the tensile properties of Al-7Si-0.4Mg alloys in terms of defect susceptibility due to the existence of casting defects. Tensile specimens were fabricated via gravity casting using commercial A356 aluminum alloy, and the area fraction of casting defects was measured using scanning electron microscope (SEM) fractographic analysis of the tensile fracture surfaces. Shrinkage voids and oxide bifilms are representative casting defects that significantly influence the tensile properties of A356 alloys. When oxide bifilms are present alongside shrinkage voids, tensile properties exhibit greater sensitivity to changes in the area fraction of casting defects compared to specimens containing only micro-voids in the form of shrinkage voids containing a thin oxide film. However, the defect susceptibility coefficients for tensile strength and elongation under T6-treated conditions are somewhat lower than those observed in the as-cast specimens. In this study, the area fraction of oxide bifilms on the fracture surfaces of the tensile specimens averaged 12.5%, with an inclusion frequency of approximately 45%, which is relatively lower than that of shrinkage voids present on all fracture surfaces. The defect susceptibility coefficients for tensile strength and elongation in as-cast specimens where the casting defects consisted solely of oxide bifilms were approximately 3.58 and 11.34, respectively. These values represent clear increases of approximately 3.2 and 9.1 compared to specimens containing only shrinkage voids; a similar trend was observed under T6-treated conditions.
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Figures(9) / Tables(4)
Choongdo Lee. Relative contribution of oxide bifilms and micro-voids to tensile property of Al-7Si-0.4Mg alloys[J]. AIMS Materials Science, 2026, 13(2): 282-299. doi: 10.3934/matersci.2026016
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