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.

Investigation of the Electrochemical Corrosion Property of 2xxx Series Cast Aluminium Alloy in 0.3 M, 0.6 M NaCl, and Seawater Environments

“…Afterward, the solutionized samples were subjected to machining to produce 5 mm × 5 mm × 12 mm rectangular samples. They were kept at 200 °C for 240 mins to gain the peak aged condition [13]. The surfaces were polished with emery papers of 320, 600, 800, 1200, and 2000 grit sizes to get a smooth surface finish.…”

“…In the potentiodynamic polarization technique, a potential difference is applied between the working and reference electrodes, and the produced current is measured, which represents the corrosion rate occurring on the exposed surface of the working electrode. The electrochemical corrosion behavior of aluminum alloys in different media is being investigated [13]. Adams et al conducted an experimental study adopting the polarization technique and microstructural characterization to understand the corrosion behavior of AA8011, AA4017, and AA1200 aluminum alloys exposed to nitric and acetic acid media and concluded that passive films that are formed in nitric acid are more stable than in acetic acid solution [14].…”

Investigation on electrochemical corrosion behavior of eutectic Al-Si automotive alloy in 0.2 M HCl, 0.2 M NaOH, and 0.2 M NaCl environments

“…In case of HCl and NaCl environment, higher corrosion resistance is found in higher silicon added alloy as Si forms Mg 2 Si intermetallic phase with Mg, which is anodic to the aluminium matrix and may enhance the corrosion resistance of the alloys to some extent. The Mg 2 Si precipitations form SiO 2 and MgO [22,43,44]. However, in NaOH there is higher rate of H 2 generation on the exposed surfaces of the alloy with eutectic amount of Si, which may be responsible for the increased corrosion [39].…”

“…are added as alloying elements in the alloy matrix to upgrade various mechanical and physical properties of aluminum alloys [20]. Silicon as an alloying element improves not only strength but surface quality, corrosion resistance, hardness and other properties in the alloy [21,22]. The eutectic system of Al-Si has two solid phases, of which the eutectic composition is 12.2 ± 0.1 wt.…”

“…Recently, some studies are going on evaluating the corrosion resistance of these alloys in different media [27,28]. Again, the role of Si on electrochemical corrosion performance in NaCl solution has been studied previously [22]. Therefore, the objective of this exercise is to understand the corrosion nature of Al-Si alloy with eutectic composition of Si (12.7 wt.…”