The Impact of Machining on the Corrosion Behaviour of AA7150-T651 Aluminium Alloy

Abstract

In the present study, the corrosion behaviour of machined AA7150-T651 aluminium alloy has been investigated. It was revealed that a near-surface deformed layer with thickness of 500 nm, characterized by ultrafine grains, is present between the alloy surface and the bulk alloy. In the deformed layer, the MgZn2 precipitates were absent, while segregation bands developed at the grain boundaries. The presence of the segregation bands, rich in magnesium and zinc, promoted localized corrosion in the deformed layer. Potentiodynamic polarization of the alloy in deaerated 3.5 wt. % sodium chloride solution revealed current surges at potentials of-750 mV (SCE) and-670 mV (SCE) respectively. The second current surge was associated with the fast dissolution of the deformed layer. Immersion testing of the alloy in 3.5 wt. % sodium chloride solution showed that the deformed layer acted as anode while the bulk alloy served as cathode during corrosion process.