Effect of microstructure on corrosion of cast aluminium alloys

Sammanfattning

This project explores the impact of microstructure on the corrosion behaviour of cast aluminium-silicon alloys, in both primary and recycled variants of the AlSi7-alloy. It evaluates the influence of composition of the alloy and surface condition on corrosion resistance by comparing as-cast skin and polished samples. Four aluminium alloys are examined: one primary alloy and three secondary variants with varying levels of iron, zinc, cooper, and vanadium content. Microstructural characterization is performed using optical microscope, scanning electron (SEM), optical emission spectroscopy (OES), and image analysis to identify the phases of the alloys. Corrosion behaviour is examined using polarization testing and statistical analysis of pitting corrosion, with salt spray exposure used specifically to evaluate pit formation. The results reveal that alloying elements significantly influence intermetallic compounds formation and the characteristics of corrosion pits, such as their depth or distribution in the sample. The comparison between as-cast skin and polished samples revealed that surface condition has a significant role in corrosion behaviour. As-cast skin samples displayed distinct corrosion characteristics compared to polished ones. These findings highlight the importance of both composition and surface treatment in optimizing the corrosion resistance of recycled aluminium alloys.