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 Al ₂ Cu-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} _α planes. Subsequently, the bands develop into gross pitting driven by the solution acidification and redeposition of thermodynamically nobler Cu, forming the Cu-matrix couples.