Li reactivity during the surface pretreatment of Al-Li alloy AA2050-T3

The dissolution of aluminum alloy AA2050-T3 (which contains 0.77 wt.% Li) during a chemical pretreatment sequence was investigated. Atomic emission spectroelectrochemistry (AESEC) was used to quantitatively measure the dissolution rates of individual alloying elements during a complete pretreatment sequence. The results reveal significant Li and Al dissolution, and Cu enrichment during NaOH exposure. When the alloy was exposed to HNO3, excess Cu was preferentially dissolved in addition to the dissolution of Fe, Mn and Mg. Polarization testing in conjunction with on-line AESEC reveal a decrease in both anodic and cathodic currents, along with an increase in the alloy pitting potential, following pretreatment. In addition, what appears to be a protective Li/AI surface film was also determined to exist with GDOES surface profiles following polarization as indicated by an increase in the surface Li/Al ratio and which favors the formation of insoluble Al species during anodic polarization in neutral electrolyte and strongly suggests a stabilizing effect of Li on the Al passive film. Beyond the context of surface pretreatment, which is necessary precursor to conversion coating, the study herein also provides significant insights into the corrosion of AA2050-T3 - including selective dissolution and its attendant rate - which are previously unreported. (C) 2017 Elsevier Ltd. All rights reserved.