The Role of Cu-Based Intermetallic on the Direct Growth of a ZnAl LDH Film on AA2024

abstract

The direct ZnAl layered double hydroxide growth on AA2024 is a fast-occurring reaction, yet is characterized by an inhomogeneous film thickness. It has been shown that at the periphery of Cu-rich intermetallic, the flakes tend to be larger and denser. A combination of in situ and ex situ measurements were used to monitor the changes in the layered double hydroxide film grown on the regions of intermetallics. Immediately after immersion, an activation of the intermetallic phases is observed due to the dealloying process with an almost immediate film growth. Dealloying is followed by trenching of the adjacent Al matrix leading to an excessive production of large and dense layered double hydroxide flakes at the periphery of the intermetallic. However, the scanning electron microscopy cross-section images revealed that the trenching process leads to defects in the area surrounding the intermetallic. This could weaken the corrosion resistance performance of the layered double hydroxide conversion coating and lead to adhesion failure of consecutive polymer coatings. Nevertheless, this work highlights a few advantages and drawbacks of the layered double hydroxide conversion coatings and pathways to its potential optimization and improvement.

keywords

CHROMATE CONVERSION COATINGS; ACTIVE CORROSION PROTECTION; ALUMINUM-ALLOYS; HEXAVALENT CHROMIUM; COPPER DISSOLUTION; MECHANISM; RAMAN; NITRATE; PERFORMANCE; LAYER

subject category

Electrochemistry; Materials Science

authors

Bouali, AC; Serdechnova, M; Yasakau, KA; Lutz, A; Wiese, G; Terryn, H; Ferreira, MGS; Zheludkevich, ML

Groups

G3 - Electrochemical Materials, Interfaces and Coatings

Projects

Projeto de Investigação Exploratória: Kyril Yasakao (IF/01284/2015)

CICECO - Aveiro Institute of Materials (UIDB/50011/2020)

CICECO - Aveiro Institute of Materials (UIDP/50011/2020)

Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)

acknowledgements

ACB would like to thank the EFC young scientist for awarding the EUROCORR Young Scientist Grant 2017, financially supporting her research stay among the SURF group at Vrije Universiteit Brussel and accomplishing a part of the current study. ACB is also grateful to Kitty Baert and Priya Laha for their assistance and technical support during her stay at the SURF group. MS and MLZ are thankful to I2B fond for the financial support of this work in frame of MUFfin project. KY acknowledges the Portuguese Foundation for Science and Technology for the researcher grant (IF/01284/2015). Both KY and MGSF are also grateful to the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020 & UIDP/50011/2020, financed by national funds through the Portuguese Foundation for Science and Technology/MCTES. Additionally MGSF wishes to separately acknowledge LA/P/0006/2020 also financed by national funds through the FCT/MEC (PIDDAC). AL also acknowledges the financial support of VLAIO (Grant nr. HBC.2017.0300).