The effect of solidification cooling rate (2.7, 5.5, 17.1, and 57.5 C/s) was studied on the microstructure and corrosion behavior of Al-15Mg2Si composite. The results showed that a higher solidification cooling rate decreased the size of Mg2Si particles and changed their morphology to more compact forms. Increasing the solidification cooling rate also improved the distribution of microconstituents, refined the grains, and reduced the micropores fraction. A direct correlation between the microstructural characteristics dictated by the cooling rate and the corrosion resistance of the composites was found. The electrochemical impedance spectroscopy tests showed that the sample with the highest solidification cooling rate had a corrosion resistance of about 2.5 times higher than the slowly cooled one. Accordingly, the potentiodynamic polarization tests showed that the corrosion current density of the former sample was about 1.5 times lower than that of the latter. A finer microstructure obtained at higher solidification cooling rates led to higher corrosion resistance possibly because a more integrated passive film formed on the surface.
