Pitting corrosion of aluminum

Colorimetric metal ion sensors – A comprehensive review of the years 2011–2016

Active corrosion protection and corrosion sensing in chromate-free organic coatings

Triazole and thiazole derivatives as corrosion inhibitors for AA2024 aluminium alloy

Various effects of chromate conversion coatings (CCCs) and chromate in solution on the corrosion of AA2024-T3 and pure Al are studied in this work. Raman spectroscopy was used to investigate the nature of chromate in CCCs through a comparison with the spectra of known standards and artificial Cr(III)/Cr(VI) mixed oxides. Chromate was shown to be released from CCCs and to migrate to and protect a nearby, uncoated area in the artificial scratch cell. However, experiments investigating the effect of chromate in solution on anodic dissolution kinetics under potentiostatic control indicated that large chromate concentrations were needed to have an effect.

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Effects of chromate and chromate conversion coatings on corrosion of aluminum alloy 2024-T3

The growth of pits in 209 nm thick Al films in chloride solutions with and without dichromate ions was examined using image analysis of the growing pits to determine pit current density. In pure chloride solutions, the pit current density decreased at high potentials after reaching a maximum value, and then was almost independent of applied potential. A hysteresis in the pit current density-potential behavior was observed during downward stepping of the potential from high values. This is a result of a combination of supersaturation of the pit electrolyte followed by salt film formation, and changes in mass transport from hydrogen bubbles that increase convection and lift the remnant passive film away from the dissolving surface. In solutions containing dichromate ions, the corrosion and repassivation potentials shifted in the noble direction, and rather large metastable pits formed at the open circuit. A large concentration of dichromate ions was needed to inhibit pit growth. In dichromate solutions, subsequent pit growth at higher potentials often initiated at the edge of the open-circuit pits. The rate of pit growth was lower for these pits because the remnant passive film layer was not easily lifted up at these sites, and thus created a barrier for mass transport away from the dissolving pit edge.

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D. Lu

Papers

Effects of chromate and chromate conversion coatings on corrosion of aluminum alloy 2024-T3

Pitting in Aluminum Thin Films Supersaturation and Effects of Dichromate Ions