The Effect of Surface Pretreatment of Aluminum Alloy 7075-T6 on the Subsequent Inhibition by Cerium(III) Acetate in Chloride-Containing Solution

Abstract

The study aimed to investigate the effect of surface pretreatment on the corrosion protection of aluminum alloy 7075-T6 in sodium chloride solution using cerium acetate as a corrosion inhibitor. Different surface pretreatments were tested: (i) mechanical grinding, (ii) mechanical grinding and non-water diamond polishing, (iii) mechanical grinding, alkaline etching with NaOH and acid desmutting, and (iv) mechanical grinding, alkaline cleaning with a commercial SurTec cleaner and acid desmutting. Topography, composition, and morphology of inhibited surface during immersion were investigated using optical microscopy, 3-D profilometry, scanning electron microscopy/energy-dispersive X-ray analysis and Fourier transform infrared spectrometry. The corrosion properties were determined by potentiodynamic measurements and electrochemical impedance spectroscopy in sodium chloride solution without and with the addition of cerium acetate. A change in the composition and morphology of the inhibited surface was noticed as a function of surface pretreatment and immersion time. Appropriate surface treatment resulted in improved protection against localized corrosion even after long-term immersion up to 1 month. Among mechanical pretreatments, polishing gave better results than grinding. Among chemical pretreatments, alkaline cleaning in SurTec/HNO 3 was more appropriate as a preceding step to acid desmutting than alkaline etching with NaOH.