Application of Electrochemical Noise Analysis for Rapid Assessment of Corrosion Resistance in Anodized AlSi Alloys

Aluminum-Silicon (AlSi) alloys are widely used in the automotive industry due to their excellent combination of low density, castability and mechanical properties. However, AlSi alloys are characterized by a native Aluminum oxide layer, only a few nanometers thick, which provides insufficient protection against corrosive environments. Anodizing is widely recognized as an effective strategy to enhance the corrosion resistance of AlSi alloys by forming a thick, micrometric Aluminum oxide layer. The capability of the anodic layer, as obtained using anodizing, to protect against corrosive media, is typically evaluated using Neutral Salt Spray (NSS) tests, in accordance with ISO 9227:2022. This type of test is based on the visual evaluation of the aesthetic appearance of the corroded components and is therefore strongly affected by a certain degree of subjectivity. In addition, NSS tests typically require hundreds of hours, thus imposing significant time constraints on the validation of corrosion-resistant components. As a consequence, there is a strong need for a fully quantitative and rapid method to evaluate the corrosion resistance of anodized AlSi- based components. In this context, this work proposes the use of Electrochemical Noise Measurements (ENM) as a quantitative method for corrosion resistance assessment, to be correlated with the results of NSS tests. The aim is to provide a faster and fully quantitative approach for evaluating the corrosion resistance of anodized AlSi alloys. According to these premises, EN-AC 45300 (AlSi5CuMg) specimens are anodized to obtain different anodic layer thicknesses and tested using both ENM and NSS methods to establish a correlation. The results demonstrated a clear relationship between anodic layer thickness, the logarithm of the noise resistance (Rn), as obtained using ENM, and the number of hours to failure in NSS testing. Taken together, the results demonstrate that the corrosion resistance of anodized AlSi-based automotive components can be rapidly predicted using accurate and fully quantitative electrochemical techniques.