Towards understanding micro-galvanic activities in localised corrosion of AA2099 aluminium alloy

The micro-galvanic interactions between Cu-Fe-Mn-Li-containing aluminides and the alloy matrix of aluminium alloy AA2099 during chloride-induced corrosion were investigated in-situ with real-time monitoring of the local contact potential difference (V_CPD) using the scanning Kelvin probe force microscopy (SKPFM) at controlled relative humidities. The aluminides showed noble potentials and were able to ennoble their neighbouring matrix sites when a cluster of aluminides surrounded the matrix. The matrix, hence, adopted a more positive V_CPD, towards that of the aluminides. The anode-to-cathode ratio changed throughout the corrosion exposure and was seen to show a dynamic character. Much higher local V_CPD activities were recorded during the earliest stages of corrosion, when the Al-Li AA2099 surface was first exposed to high humidities, than in later RH cycles; a phenomenon not seen in other aluminium alloys.