Origin of the Zn-induced Al intergranular corrosion of the outermost surface layer of the aluminium grain boundary: An ab initio study

The effects of zinc segregation on intergranular corrosion of the outermost surface layer of the Al Sigma 5 (012)/[100] grain boundary (GB) in an aluminium alloy have been investigated based on first-principles density functional calculations. It is demonstrated that the outermost surface of an Al GB with Zn atom segregation is less stable than that of the pure Al GB, and the first or second nearest-neighbour Al atom of a segregated Zn atom is more prone to corrosion dissolution than those in other sites. The electronic structure analysis shows that a charge reduction region forms along the grain boundary, which causes a more negative electrode potential shift than the pure Al GB. The Zn-Al bond has a metallic character that is similar to the Al-Al bond regardless of the degree of Zn segregation. It is confirmed that the corrosion of the outermost surface of the Al grain boundary with Zn segregation is enhanced because of the charge depletion among Al atoms and Zn atoms. This work contributes to our understanding of the comprehensive effects of Zn segregation on stress corrosion cracking of aluminium alloys. (C) 2015 Elsevier B.V. All rights reserved.