Effect of different chloride environments on corrosion behavior of secondary AlSi7Mg0.6 cast alloy with higher Fe content

Abstract

Secondary aluminum alloys are materials with higher Fe content. There are currently several studies on the corrosion behavior of casts from metal molds, but sand casts are being forgotten despite being still primarily used in gravity casting. Secondary Al-alloys have exceptional benefits as they are made from scrap and can be cast as thin-walled, which has a positive effect on the lightening of constructions, and on environmental impact. Unfortunately, the Fe is a common impurity but in higher content decrease properties of aluminum casts. The removal of the Fe content is very expensive, and therefore the effect of Fe content in a larger amount is monitored. This work is focused on the corrosion behavior of the heat-hardening aluminum alloys commonly used to produce castings AlSi7Mg0.6 for automotive. The experimental alloy was intentionally contaminated with Fe for reaching the critical amount of Fe in aluminum casts. Metallographic analysis (using optical and scanning electron microscopy, energy dispersive X-ray analysis) was used before corrosion tests. The microstructure of experimental alloys with higher content of Fe contains large Fe-rich phases in the form of needles. These changes in microstructure lead to the formation of a higher amount and size of porosity but the α-phase was not affected. Corrosion properties were examined by three basic corrosion tests: immersion test, potentiodynamic test, and Audi test. Corrosion characteristics of materials were evaluated using a stereo and optical microscope. Corrosion evaluation of the alloys shows the presence of pitting corrosion, which increases with increasing Fe content.