Microstructure Analysis of Progressive Secondary AlSi7Mg0.6 Alloy with Higher Fe Content Using Electron Metallography Techniques

Abstract

This article investigates the effect of the higher Fe content on the formation of brittle Fe-rich needle-like phases in heat-treated secondary AlSi7Mg0.6 cast alloy. These secondary-recycled alloys contain an increased amount of impurities due to remelting of scrap. The common unwanted impurity found in these alloys is Fe. Its higher content negatively affects the structure and mechanical properties. Fe has low solubility in Al-alloys thus forming unwanted intermetallic phases such as β-Al5FeSi. Fe cannot be removed in the foundry conditions, so its content is reduced to an acceptable limit. One of the possibilities to eliminate the negative effect of high Fe content on the structure and mechanical properties is heat treatment. Heat treatment influences the size and morphology of structural components, which leads to a finer structure and thus better mechanical properties. Therefore, this study is focused on the changes in structure depending on the Fe content influenced by heat treatment applied to the secondary AlSi7Mg0.6 alloy with higher Fe content and evaluation using a scanning electron microscope, including methods of EDX analysis, and methods of deep etching.