Abstract
Surface pretreatment coatings are a research area in continuous transformation. Moving away from the well-known chromium conversion coatings (CCC) toward an environment-friendly alternative is of great interest. Materials such as the aluminum alloy 2024-T3 (AA2024-T3) used in aircraft, for example, provide good mechanical performance but lack good corrosion resistance. Here, we present a polymer-clay coating made from branched polyethylenimine (BPEI) and montmorillonite (MMT) clay as a potential CCC substitute, and we examine this for the corrosion protection of AA2024-T3. This polymer-clay coating is applied by airbrushing an aqueous BPEI/MMT mixture onto any substrate. With this approach, application time is significantly reduced in comparison to other techniques (e.g. layer-by-layer assembly), and the structure of the polymer-clay coating is finely tuned by controlling the polymer-clay ratio. Results from electrochemical measurements and salt spray testing reveal good long-term (40d) corrosion protection of AA2024-T3 provided by a 1.8 μm thick coating with a 20:80 polymer-clay ratio. This polymer-clay ratio yields a highly ordered multilayered brick and mortar structure, where MMT (bricks) provides a physical barrier for the diffusion of corrosive agents/corrosion products within the coating, and BPEI (mortar) provides structural support and decelerates the corrosion process through surface buffering.
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