A study of tensile properties in Al-Si-Cu and Al-Si-Mg alloys:: Effect of β-iron intermetallics and porosity

The effect of beta-iron intermetallics and porosity on the tensile proper-ties in cast Al-Si-Cu and Al-Si-Mg alloys were investigated for this research study, using experimental and industrial 319.2 alloys, and industrial A356.2 alloys. The results showed that the alloy ductility and ultimate tensile strength (UTS) were subject to deterioration as a result of an increase in the size of beta-iron intermetallics, most noticeable up to beta-iron intermetallic lengths of similar to 100 mu m in 319.2 alloys, or similar to 70 mu m in A356.2 alloys. An increase in the size of the porosity was also deleterious to alloy ductility and UTS. Although tensile properties are interpreted by means of UTS vs. log elongation plots in the present study, the properties for all sample conditions were best interpreted by means of log UTS vs. log elongation plots, where the properties increased linearly between conditions of low cooling rate-high Fe and high cooling rate-low Fe. The results are explained in terms of the beta-Al5FeSi platelet size and porosity values obtained. (c) 2008 Elsevier B.V. All rights reserved.