Surface Evolution and Corrosion Response of SLM–Cast Hybrid Aluminium Alloys Before and After Electrochemical Exposure

Hybrid manufacturing techniques that merge selective laser melting (SLM) with conventional casting give opportunities for engineering aluminium parts with enhanced design flexibility and performance. This study uniquely evaluates the corrosion behavior and microstructural features of each section of a hybrid aluminium component—the SLM-built region and the cast substrate—individually, rather than treating the hybrid as a single entity. Electrochemical methods, comprising open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP), were applied to determine how each region responds to corrosive environments. Complementary X-ray diffraction (XRD) identified phase composition, while scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) examined surface morphology and grain structure before and after corrosion exposure. The findings revealed that regions with finer, more evenly dispersed grain structures tended to show lower corrosion current densities and more stable passivation, while areas with coarser grains were more vulnerable to localized corrosion, likely due to microstructural irregularities that compromised the protective oxide layer. Notably, one cast substrate region exhibited the highest corrosion resistance, with a corrosion rate of 0.0548 mm/year, followed by the SLM-built zones and the other cast substrate regions, which showed corrosion rates of 0.0976, 0.1635, and 0.1873 mm/year, respectively. These findings reveal the novelty of section-specific analysis, how each section of a hybrid aluminium structure behaves differently, hence providing insight for material design and optimization.