On the role of Fe-content on the damage behavior of an Al-Si-Cu alloy

Abstract

Secondary recycled Al alloys are in the focus of industry because they possess a tremendous potential for cost and energy savings. However, they are inevitably contaminated with a certain amount of iron from which several variants of brittle intermetallic inclusions are formed. Tensile and fatigue tests were performed with specimens containing varying amounts of iron, and subsequent high resolution CT-analysis was performed in order to identify critical defect configurations. It was found that there is a certain critical amount of iron, below which the tensile strength and the ductility are affected in a minor way, if an appropriate heat treatment is performed. High resolution computer tomography shows that this is related to the fact that the most dangerous platelet-like ß-inclusions are partly dissolved in the heat treatment process. Fatigue strength, on the other hand, is influenced by two effects: First, the porosity is increases with increasing iron content, as the iron-platelets are formed at higher temperatures and hinder material flow in the casting process. Second, iron inclusions can be found in the casting skin and act as crack initiators, if the iron content exceeds a certain level.