Investigation of Electrochemical Behaviour Related to the Microstructures of Different Aluminium Alloys Used in the Automotive Industry

Aluminium casting alloys are extensively used in the automotive sector, with Al–Si–Cu systems such as A380 favoured for their excellent castability and cost-effectiveness. In contrast, Al–Cu based alloys like A206 provide superior mechanical strength but are often regarded as less corrosion resistant, restricting their use in aggressive environments. Despite their industrial relevance, a direct comparative assessment of these alloys under controlled solidification conditions remains scarce. In this study, the electrochemical behaviour of Al–5Cu (A206) and Al–8Si–3Cu (A380) alloys were systematically investigated as a function of microstructure, modified through sand and permanent mould casting. Potentiodynamic polarization tests were performed in 3.5 wt.% NaCl solution to evaluate corrosion potential (Ecorr vs. Ag/AgCl) and current density (Icorr). Microstructural characterization revealed significant dendrite refinement and reduced secondary dendrite arm spacing (SDAS) in permanent mould castings compared with sand castings. Although A380 exhibited finer SDAS than A206, its corrosion resistance was consistently inferior due to the galvanic activity between eutectic Si and Al2Cu phases. By contrast, the simpler binary microstructure of A206 limited cathodic heterogeneity, allowing refinement to translate into improved electrochemical stability. The results demonstrate that corrosion resistance in aluminium casting alloys is governed not only by microstructural parameters but also by alloy chemical composition. These findings extend current understanding of the microstructure–corrosion relationship and provide practical guidance for alloy selection in automotive applications. A206 alloy, when cast under optimized conditions, emerges as a promising candidate for structural components exposed to chloride-rich service environments.