Electrochemical corrosion performance of Si-doped Al-based automotive alloy in 0.1 M NaCl solution

Abstract

The aim of this study is to investigate the electrochemical corrosion behavior of Al-Si automotive alloys with different levels of Si doping in 0.1 M NaCl solution at room temperature. The study was performed by electrochemical method, using potentiodynamic polarization and electrochemical impedance spectroscopy techniques. The condition of surfaces was characterized by both optical and scanning electron microscopy. Both the EIS and Tafel analyses revealed that the corrosion resistance was improved with the addition of Si up to the eutectic point due to the formation of protective oxide films. The higher Si added alloys showed lower values of current density, while the corrosion potential was shifted to a more positive direction. For higher Si added alloys, a higher amount of Mg2Si was formed as precipitates, which tend to form oxides such as SiO2 and MgO, further protecting the surfaces from corrosion. It can be observed from the micrographs that the scratches from polishing are removed after corrosion. Additionally, the SEM images reveal that corroded surfaces appear to have pits that are less noticeable in alloys with a greater Si content, suggesting thus the formation of a protective layer of oxides.