Nanostructured sol-gel coatings doped with cerium nitrate as pre-treatments for AA2024-T3 Corrosion protection performance

Sol–gel derived films exhibit a high potential as substitutes for the environmentally unfriendly chromate metal-surface pre-treatment methods. Inorganic sol–gel derived films offer good adhesion between metals and organic paint. However, they cannot provide adequate corrosion protection due to their high crack-forming potential. Introduction of an organic component to an inorganic sol–gel system leads to the formation of thicker, more flexible and functionalized films with enhanced compatibility to different organic top coatings. Incorporation of nanoparticles in the hybrid sol–gel systems increases the corrosion protection properties due to lower porosity and lower cracking potential along with enhancement of the mechanical properties. Furthermore, the incorporation of inorganic nanoparticles can be a way to insert corrosion inhibitors, preparing inhibitor nanoreservoirs for “self-repairing” pre-treatments with controlled release properties.

Sol–gel coatings for corrosion protection of metals

Phosphonium cation-based ionic liquids (ILs) are a readily available family of ILs that in some applications offer superior properties as compared to nitrogen cation-based ILs. Applications recently investigated include their use as extraction solvents, chemical synthesis solvents, electrolytes in batteries and super-capacitors, and in corrosion protection. At the same time the range of cation–anion combinations available commercially has also been increasing in recent years. Here, we provide an overview of the properties of these interesting materials and the applications in which they are appearing.

Phosphonium-Based Ionic Liquids: An Overview

Plasma electrolytic oxidation of magnesium and its alloys: Mechanism, properties and applications

The corrosion susceptibility of Mg and its alloys in humid and aqueous environments limits their widespread application. The performance of several conversion coating technologies is reviewed herein. In addition to the assessment of performance based on the literature to date, thermodynamic analysis has been used to compare coating processes. Ongoing research reveals that the search for appropriate conversion coatings to replace toxic Cr-based coatings continues. It is seen that the variability between coatings of the same technology was greater than the averages between coating technologies. Additionally, coating pretreatment also appears to be more significant than the choice of coating technology itself.

Review of Corrosion-Resistant Conversion Coatings for Magnesium and Its Alloys

A CeCl 3 /H 2 O 2 aqueous solution treatment is assessed for the formation of conversion coatings on a AZ63 magnesium alloy. The coating composition and morphology are examined. The conversion coating appears to consist of a thin and cracked coating with ‘dry-mud’ morphology with large agglomerates over cathodic intermetallic particles. The corrosion resistance in NaCl solution has been investigated. The cerium-based conversion process improves the pitting potential of the alloy. Better corrosion resistant surfaces are obtained when the samples are submitted to repeated immersions in the conversion bath for 30 s up to 180 s of total immersion time. The thickness of the cerium conversion coating rapidly grows up in the first 30 s; afterwards it remains nearly constant. An increase of both hydrogen peroxide concentration and immersion time produces a worsening of the alloy to corrosion.

Cerium based chemical conversion coating on AZ63 magnesium alloy

Effect of HCl pre-treatment on corrosion resistance of cerium-based conversion coatings on magnesium and magnesium alloys

In this paper the effect of several parameters, such as temperature, time of immersion, cerium ions and hydrogen peroxide concentration, pH of the conversion solution, on the composition and morphology of the conversion layer are investigated as well as on its corrosion resistance in chloride environments. The cerium-based chemical conversion coatings ennobles the corrosion potential and inhibits both the cathodic and anodic reactions rate. Using a cerium (III) chloride solution a not homogeneous coating is obtained and agglomerates with a “dry-mud” morphology of mixed cerium-aluminium oxide are deposited above the cathodic intermetallic particles, while using a cerium (III) nitrate solution the coating is more uniform but thinner than that obtained with cerium (III) chloride. Solution temperature below 50°C and time of immersion of 10 minutes produces a coating with better corrosion resistance.

M. Magrini

Papers

Cerium based chemical conversion coating on AZ63 magnesium alloy

Effect of HCl pre-treatment on corrosion resistance of cerium-based conversion coatings on magnesium and magnesium alloys

Corrosion resistance of cerium‐based chemical conversion coatings on AA5083 aluminium alloy

Surface properties of AZ91 magnesium alloy after PEO treatment using molybdate salts and low current densities

Antifouling properties of different Plasma Electrolytic Oxidation coatings on 7075 aluminium alloy