Correlation Between Unsteady-State Solidification and Electrochemical Corrosion Parameters of an AlSiMg Alloy

Abstract

Electrochemical corrosion tests were performed on samples of horizontally solidified Al7Si0.3Mg (wt%) alloy. The investigated solidification and corrosion parameters were growth and cooling rates (VL and TR, respectively), secondary dendritic spacing (λ2), corrosion potential, and corrosion current (ECORR and iCORR, respectively). Optical and scanning electron microscopy analysis were carried out on the samples, and typical solidification microstructure was characterized by primary and eutectic phases (Alα and Alα-eutectic+ Si+ π-Al8Mg3FeSi6+θ-Mg2Si, respectively). The results depicted a higher corrosion resistance in as-cast samples with finer dendritic microstructure, that is, for higher and lower VL/TR and λ2 values, respectively. A mathematical expression characterized the iCORR variation with VL, TR, and λ2. SEM/EDS element maps and point microanalysis showed a strong decreased of Mg and Fe elements within the interdendritic regions due to the corrosion of π and θ intermetallic phases. It was allowed to conclude that Si particles exhibit cathodic behavior in relation to the matrix as well as π and θ intermetallic compounds. A comparative analysis with the literature was also conducted. Graphic Abstract: [Figure not available: see fulltext.].