Role of intermetallic phases in initiation and propagation of intergranular corrosion of an Al-Li-Cu-Mg alloy

TL;DR

This study investigates how intermetallic phases influence the initiation and spread of intergranular corrosion in an Al-Li-Cu-Mg alloy, revealing the electrochemical activity of specific phases and their role in corrosion mechanisms.

Contribution

It provides new insights into the corrosion behavior of intermetallic phases in Al-Li-Cu-Mg alloys, highlighting their electrochemical activity and impact on corrosion propagation.

Findings

Intermetallic phases containing Li are electrochemically active and prone to self-dissolution.

Corrosion initiates at trenching in the Al matrix near Al7Cu2(Fe, Mn) particles.

Corrosion propagates via micro-galvanic interactions along particle-matrix interfaces.

Abstract

Intermetallic phases in a recently developed Al-Li-Cu-Mg alloy have been investigated to understand their roles in the initiation and propagation processes of intergranular corrosion. Corrosion initiation involves trenching formation in the Al matrix adjacent to the large particles of Al7Cu2(Fe, Mn) phases. These phases containing Li are electrochemically active and susceptible to self-dissolution via a de-alloying mechanism during corrosion process. The subsurface particles of Al7Cu2(Fe, Mn) and Al20Cu2Mn3 phases act as the internal cathodes for continuous corrosion propagation along the particle-matrix interface and the associated grain boundaries. Corrosion propagation along the particle-matrix interface was facilitated by the anodic dissolution of the surrounding Al matrix due to the micro-galvanic interaction with the cathodic intermetallic phases. In addition, T1 (Al2CuLi) precipitates and the isolated particles of Al7Cu2(Fe, Mn) and Al20Cu2Mn3 phases were dissolved along the path of corrosion propagation. The dissolved metal ions were redeposited through the network of crevice.