In-situ monitoring of alloy dissolution and residual film formation during the pretreatment of al-alloy AA2024-T3

The dissolution of intermetallic phases in AA 2024-T3 aluminum alloy sheet was investigated during a coating pretreatment sequence. The atomic emission spectroelectrochemistry (AESEC) technique was used to quantitatively measure the dissolution rates of individual alloying elements during a complete pretreatment sequence. The results demonstrate the significant selective dissolution of Al in 1.25 M NaOH, leading to the enrichment of alloying elements such as Cu. Subsequent 2.8 M HNO₃ treatment contributes toward dissolving the excess residual layer and passivates the alloy matrix, however the presence of a residual Cu layer at the alloy surface was evidenced. The real-time alloy dissolution profiles are presented herein, and discussed in the context of the surface morphology via microscopy.