Improvement of corrosion resistance in high-strength Al–Si–Cu–Mg casting alloy is an important issue for its application in humid and corrosion environment. In this paper, the effect of Cr on microstructure, mechanical properties and corrosion behavior of Al–9Si-1.2Cu-0.5 Mg alloy were investigated. The results indicate that 0.052 % and 0.106 % Cr addition shows a slight strengthening for mechanical properties by introducing AlSiFeCr dispersoids, 0.052 % Cr addition effectively enhances the corrosion resistance of the alloy. The addition of 0.052%Cr not only increase the thickness and stability of the passive film, but also has an obvious effect on the charge transfer process. 0.052 % Cr addition reduces the potential difference between cathode phases and Al matrix. The results of first-principles calculations indicate that the (001) surface of CrO2 would have an effect of adsorbing Cl− ions in the passive film/solution interface, the interaction between Cl and neighboring Cr atoms implies the formation of chemical bonds between Cl atoms and the surrounding Cr atoms at adsorption sites. It contributes to weaken the attack of the passive film by Cl− ions. When Cr level increases to 0.106 %, the appearance of AlSiFeCr dispersoids may result in the additional electrochemical process and weaken the protection on the matrix. This paper designs a novel Al–Si–Cu–Mg–Cr casting alloy with high mechanical properties and high corrosion resistance, expanding automotive industry application of casting aluminum alloy.
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