Layered double hydroxide based active corrosion protective sealing of plasma electrolytic oxidation/sol-gel composite coating on AA2024

A.C Bouali,E.A Straumal,M Serdechnova,D.C.F Wieland,M Starykevich,C Blawert,J.U Hammel,S.A Lermontov,M.G.S Ferreira,M.L Zheludkevich

doi:10.1016/j.apsusc.2019.07.117

A.C Bouali, E.A Straumal + Show 8 more

Open Access

https://doi.org/10.1016/j.apsusc.2019.07.117

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Abstract

This work reports a novel approach for growing layered double hydroxide (LDH) films on any plasma electrolytic oxidation (PEO) coated AA2024 independently of the nature of the PEO coating. The specific PEO coating chosen to carry out this work is considered to be not suitable for direct LDH growth because of phase composition and morphological features. In this paper, we describe a new methodology that consists of covering the PEO coating with a thin layer of aluminum oxide based xerogel as the source of aluminate ions for subsequent in-situ LDH growth. X-ray diffraction (XRD) and scanning electron microscope (SEM) images showed a successful formation of LDHs on the surface. An improvement in terms of active corrosion protection was also demonstrated by electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET).

Highlights

Plasma electrolytic oxidation is a green anodizing process using micro-discharges to produce hard and dense ceramic-like coatings with a good wear and corrosion resistance [1,2,3]
A novel approach of achieving active corrosion protection by means of layered double hydroxide (LDH) conversion sealing for plasma electrolytic oxidation (PEO) coatings has been proposed in this work
The possibility to expand the use of LDH-based sealing for different PEO coatings, regardless of their morphologies and phase composition, was demonstrated

Summary

Introduction

Plasma electrolytic oxidation is a green anodizing process using micro-discharges to produce hard and dense ceramic-like coatings with a good wear and corrosion resistance [1,2,3]. The discharges are responsible for creating defects and pores that can lead to a decrease of the barrier properties provided by the coatings and their failure in long-term corrosion protection Different methods such as optimization of the process parameters (variation of voltage/current magnitude, mode, frequency and duty cycle) [4,5,6] on one hand and the addition of various particles into the electrolyte on the other hand, have been investigated to overcome the problem [8]. An additional sol-gel based post-processing was applied in order to create an aluminum oxide based xerogel layer [29,30] offering a new source of Al(OH)4- anions for the formation of LDH nanocontainers In this respect, the concept of combining high barrier properties of a thicker PEO coating and active corrosion protection provided by the LDH loaded with corrosion inhibitors (vanadate was used in frame of this work as a model corrosion inhibitor) should be achieved

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