Effect of key alloying elements on the feeding characteristics of aluminum–silicon casting alloys

Abstract

The most common and serious defect in aluminum castings is porosity, which is a result of two phenomena, insufficient feeding and/or hydrogen precipitation during solidification. These defects cause costly scrap loss and limit the use of castings in critical, high-strength applications. In this paper, the effect of alloying elements Si, Fe, Mg, Mn, Cu, Sr, and Ti as well as the cooling rate on the amount of porosity retained in aluminum castings has been quantified. The density of samples taken from locations along the length of a plate cast in sand is measured using Archimedes' principle following ASTM procedures. Hot isostatically pressed samples are used to determine the theoretical density of each of the alloys. The percent porosity is calculated from the difference between theoretical and measured density. The relative contribution of each of the alloying elements to porosity formation is calculated using analysis of variance. Scanning electron microscopy of some samples is performed to correlate the results obtained from analysis of variance to the intermetallics formed. It is observed that the morphology of the intermetallics greatly affects feedability of the alloy.