Finite Element Modeling of Chemical and Electrochemical Protection Mechanisms Offered by Mg-Based Organic Coatings to AA2024-T351

Abstract

A finite element model of the protection mechanisms offered by Mg-based organic coatings was developed. The model predicted the change in the corrosion potential of AA2024-T351 as a function of pH, water layer thickness, and the inhibition of oxygen reduction reaction. The pH in the solution was calculated taking into account Mg dissolution, precipitation of Mg(OH)2, Al dissolution, and hydrolysis of Al3+ ions. The predicted critical pH value at which the corrosion potential of AA2024-T351 sharply decreases to values below pitting and pit repassivation potentials under full immersion conditions was in accordance with experimental observations. A limiting water layer thickness below which the pH-induced pit repassivation mechanism is not predicted to occur was calculated. If the inhibition of oxygen reduction reaction by Mg(OH)2 is considered, the pH-induced repassivation mechanism becomes feasible at thinner water layers. Cathodic protection offered by Mg-rich primers was modeled as a function of coating resistance, water layer thickness, and electrolyte chemistry. The magnitude of the resistance of the film in which Mg pigments are embedded mitigates the extent of the cathodic protection. The change in local pH due to corrosion reactions affected the galvanic potentials obtained. The framework developed can be used to help identify chemical inhibitors that can operate by the chemical protection mode described in this work.

Application of Finite Element Modeling to Macro-Galvanic Coupling of AA7050 and SS316: Validation Using the Scanning Vibrating Electrode Technique

“…For such cases, transient models that take into account the evolving electrolyte chemistry and its effect on the electrochemical behavior of the alloys can improve the predictability of the computational approach. 36 Advantages of combining the SVET and computational techniques.-The advantages of combining SVET with FEM approaches have been discussed in the literature, and both techniques have been combined to investigate the galvanic coupling behavior between dissimilar alloys. 16,24,26,27,[29][30][31][32]46 As stated previously, the SVET tip herein measured the potential difference at 85 μm and 115 μm over the entire surface.…”

“…Recent work in the literature have utilized FEM to investigate the effects of corrosion products on micro-and macrogalvanic corrosion. 36,[50][51][52] Understanding the complex precipitation reactions and how they may contribute in stifling localized corrosion, is an area of future work. In addition, sites with copper replating could switch their behavior from anodic to cathodic, which was not accounted for in the present model.…”

“…When solving for the variables that describe corrosion phenomena in FEM with any of the governing equations above, it is common to use a scaffolding approach to determine the correct boundary conditions by starting with simplifying assumptions and working towards a more realistic scenario. 27,[34][35][36] As noted previously, computational results depend highly on the choice of boundary conditions, which are also dependent on a variety of environmental factors. 33 The aforementioned studies demonstrate the viability of the SVET for modeling galvanic corrosion processes and, to the best of the authors' knowledge, no studies in the available literature have combined these techniques with a focus on AA-SS galvanicallycoupled systems.…”

Laying the experimental foundation for corrosion inhibitor discovery through machine learning

“…The third paradigm supported the mechanistic understanding gained from experiments with computational models that span a continuum to atomistic scales. Finite element method (FEM) models produced previously unattainable information-such as mechanical strains observed for inhibitor dissolution and leaching from coatings 47 , local critical pH criteria for pit repassivation 48 , and the effect of surface geometry on electrochemical behaviour 49 . Density functional theory (DFT) and molecular dynamics (MD) simulations have introduced a vast amount of quantum mechanical/chemical information that is not directly available from empirical methods, such as density of states, band gap, and other physicochemical electronic properties 50 .…”

Antireflection Property and Corrosion Resistance of Black Ceramic Superhydrophobic Coatings on Aluminum Alloy

“…[13] The most important factor limiting Al alloys presence in more applications is corrosion occurs on surface during service. To this end, microalloying, [14,15] electrochemical protection, [16,17] surface treatment, [18,19] anodic oxidation, [20,21] and other methods have been used to improve the corrosion resistance of Al alloys. While Al alloys treated by some of the above methods fail to meet the standards required in some specific environments.…”