Electrochemical Impedance Studies on the Corrosion Phenomena in Additively Manufactured Al-Si-Mg Alloys in a Chloride Environment

Abstract

This study explores how corrosion unfolds in aluminium hybrid structures created by integrating Selective Laser Melting (SLM) with conventional casting techniques. To better understand the impact of different fabrication routes, three sample configurations were considered: fully SLM-built components, cast aluminium substrates, and hybrid structures where an SLM layer was directly deposited onto a cast base. Each of these samples was inserted into a 3.5 wt.% NaCl solution and their respective electrochemical performances were evaluated via Electrochemical Impedance Spectroscopy (EIS). With an equivalent electrical circuit model, the impedance spectra were interpreted and also to capture the interfacial corrosion dynamics. The SLM-built samples depicted greater charge transfer resistance (Rct), indicating a more protective and stable passive oxide layer. On the other hand, the cast samples showed decreased impedance responses and lower Rct values, which connote a more defective or porous oxide layer and higher susceptibility to chloride-induced corrosion. While the hybrid samples showed an intermediate corrosion reaction, which is ascribed to the combined effect of the SLM-built surface and the cast substrate. A subtle reflection of interfacial galvanic interactions was detected, consequently reducing slightly their corrosion behaviour compared to the monolithic SLM sample. Additionally, to get the degradations mechanisms, post-corrosion surface characterization was carried out via Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD). In the cast and hybrid samples, localized corrosion characteristics were revealed by the SEM, and the XRD analysis affirms the variation in the oxide phases and microstructural alterations.