Wet corrosion of Al 1050 alloy in ethyl bromide-containing environment

Abstract

The natural passivity, or induced by anodizing process, does not always result in an effective corrosion barrier for aluminium when exposed to environments containing specific chemicals that can cause material degradation phenomena with localized corrosion morphology. The present work investigates the effects of ethyl bromide (EtBr), a neutral organic molecule, sometimes used as a fumigant in packaging containers, that has been recently indicated as a possible cause of corrosion in aluminium alloy components. The study was conducted on Al 1050 alloy samples in aqueous solutions of sodium sulphate at increasing EtBr concentrations, ranging from 500 to 8600 ppm. Long-term exposure tests (936 h) and electrochemical experiments (potentiodynamic and potentiostatic polarizations, as well as time-dependent corrosion potential monitoring) were carried out, together with SEM and EDS examinations of the morphology and nature of the corrosion products. The results showed that the alloy undergoes different corrosion behaviours depending on the concentration of EtBr, spanning from passivity at the lowest concentrations to pitting at the highest, passing through the initiation and propagation of crevice at intermediate EtBr contents. A crucial role of the exposure time was detected, tentatively attributed to ethyl bromide hydrolysis in aqueous solution that liberates the bromide anion that is aggressive towards the passive state of aluminium alloys.