Application of Commercial Surface Pretreatments on the Formation of Cerium Conversion Coating (CeCC) over High-Strength Aluminum Alloys 2024-T3 and 7075-T6

Abstract

The selection of appropriate surface pretreatments is one of the pending issues for the industrial application of cerium-based chemical conversion coatings (CeCC) as an alternative for toxic chromate conversion coating (CrCC). A two-step surface pretreatment based on commercial products has been successfully used here to obtain CeCC on AA2024-T3 and AA7075-T6. Specimens processed for 1 to 15 min in solutions containing CeCl3 and H2O2 have been studied by scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM-EDX), glow discharge optical emission spectroscopy (GDOES), potentiodynamic linear polarization (LP), electrochemical impedance spectroscopy (EIS), and neutral salt spray (NSS) tests. SEM-EDX showed that CeCC was firstly observed as deposits, followed by a general coverage of the surface with the formation of cracks where the coating was getting thicker. GDOES confirmed an increase of the CeCC thickness as the deposition proceed, the formation of CeCC over 7075 being faster than over 2024. There was a Ce-rich layer in both alloys and an aluminum oxide/hydroxide layer on 7075 between the upper Ce-rich layer and the aluminum matrix. According to LP and EIS, CeCC in all samples offered cathodic protection and comparable degradation in chloride-containing media. Finally, the NSS test corroborated the anti-corrosion properties of the CeCC obtained after the commercial pretreatments employed.

Corrosion protection of aluminum alloy (AA2219-T6) using sulfonic acid-doped conducting polymer coatings

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“…29 The conducting nature of both the polymers has made it possible to use them as additives of epoxy paints. PANi has appeared to be the most promising polymer matrix for protective coatings against marine corrosion due to its non-toxic nature, 13 whereas polypyrrole is used in chemical sensors, 30 batteries, 31 ion selective electrodes 32 and conducting coatings due to its high conductivity and good stability. Since the works of Mengoli 28 et al and De Berrys 16 on conducting polymers, several attempts have been made to optimize the protection efficiency of coatings and propose a comprehensive protection mechanism.…”

The influence of vibration amplitude on AA7075-T6 corrosion resistance improvement during ultrasonic-assisted burnishing

“…1,2 However, Al alloys are susceptible to corrosion due to the galvanic coupling between intermetallic particles and the aluminum matrix. [3][4][5] Moreover, various types of corrosion such as stress corrosion cracking (SCC) 6 and intergranular corrosion 7 may occur in aluminum alloys.…”

Corrosion resistance improvement of 6061 aluminum alloy by 2D ultrasonic vibrations assisted turning

“…2,3 However, the corrosion resistance of Aluminum alloys is not favorable, particularly against pitting corrosion due to the coupling of galvanic particles with the aluminum matrix. [4][5][6] The appearance of other types of corrosion, such as stress corrosion cracking (SCC) 7 and intergranular corrosion 8 are also probable in aluminum alloys. It should be noted that a combination of corrosion mechanisms (pitting, stress corrosion cracking (SCC), intergranular corrosion) usually occurs in aluminum alloys.…”