CORRELATION BETWEEN UNSTEADY-STATE SOLIDIFICATION AND ELECTROCHEMICAL CORROSION PARAMETERS OF AN ALSIMG ALLOY

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 (V-L and T-R, respectively), secondary dendritic spacing (lambda(2)), corrosion potential, and corrosion current (E-CORR and i(CORR), respectively). Optical and scanning electron microscopy analysis were carried out on the samples, and typical solidification microstructure was characterized by primary and eutectic phases (Al-alpha and Al alpha-eutectic+ Si+ pi-Al8Mg3FeSi6+theta-Mg2Si, respectively). The results depicted a higher corrosion resistance in as-cast samples with finer dendritic microstructure, that is, for higher and lower V-L/T-R and lambda(2) values, respectively. A mathematical expression characterized the i(CORR) variation with V-L, T-R, and lambda(2). 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 pi and theta intermetallic phases. It was allowed to conclude that Si particles exhibit cathodic behavior in relation to the matrix as well as pi and theta intermetallic compounds. A comparative analysis with the literature was also conducted.