Time-varying electrochemically heterogeneous entities during the micro-galvanic corrosion associated with nanoscale precipitates in an Al-Cu-Li alloy

Electrochemically heterogeneous entities were revealed to vary with time during the micro-galvanic corrosion associated with T-1 precipitates in AA2195 alloy. Microscopic analyses firstly demonstrated a Li-leaching process in the anodic T-1 precipitates at the sub-nanometer scales, which changes the micro-galvanic couples from T-1-matrix to Al2Cu-matrix. This results in an increased work function that switches the precipitates to cathodes and leads to the matrix corrosion with Al-selective dissolution, forming crystallographic corroded bands parallel to {111}(alpha) planes. Subsequently, the bands develop into gross pitting driven by the solution acidification and redeposition of thermodynamically nobler Cu, forming the Cu-matrix couples.

Automated summary

This study reveals the time-dependent behavior of electrochemically heterogeneous entities involved in the micro-galvanic corrosion of T-1 precipitates in AA2195 alloy. The findings show a Li-leaching process in the anodic T-1 precipitates at the sub-nanometer scales, leading to a transformation of the micro-galvanic couples and resulting in corrosion of the matrix with Al-selective dissolution. The corroded bands parallel to {111}(alpha) planes then develop into gross pitting driven by solution acidification and redeposition of thermodynamically nobler Cu, forming Cu-matrix couples.