Effects of Cu and Mg on Corrosion Resistance of Al-7Si Cast Alloy

The corrosion behaviors of Al-7Si cast alloys in 3.5%NaCl aqueous solution were examined by using electrochemical and immersion corrosion tests.The influence of copper(Cu) and magnesium(Mg) on the Tafel curves and electrochemical parameters,such as free corrosion potential and corrosion current densities,of Al-7Si alloys were investigated.Moreover,the mass loss and morphology of each alloy after immersion corrosion were measured and analyzed by analytical balance and scanning electron microscopy.The results indicate that all the tested alloys can be passivated rapidly,their corrosion potential drifts to negative,their corrosion current density and corrosion mass loss increase with the addition of alloy elements Cu and Mg.Compared with element Mg,element Cu has a greater effect on the corrosion resistances of Al-7Si alloy,and can convert the corrosion mechanism of the alloy from pitting corrosion into intergranular corrosion.