The Influence of PSA Pre-Anodization of AA2024 on PEO Coating Formation: Composition, Microstructure, Corrosion, and Wear Behaviors

In the frame of the current work, it was shown that plasma electrolytic oxidation (PEO) treatment can be applied on top of phosphoric sulfuric acid (PSA) anodized aluminum alloy AA2024. Being hard and well-adherent to the substrate, PEO layers improve both corrosion and wear resistance of the material. To facilitate PEO formation and achieve a dense layer, the systematic analysis of PEO layer formation on the preliminary PSA anodized layer was performed in this work. The microstructure, morphology, and composition of formed PEO coatings were investigated using scanning electron microscopy (SEM), x-ray diffraction (XRD), and glow-discharge optical emission spectroscopy (GDOES). It was shown that under constant current treatment conditions, the PSA layer survived under the applied voltage of 350 V, whilst 400 V was an intermediate stage; and under 450 V, the PSA layer was fully converted after 5 min of the treatment. The comparison test with PEO formation on the bare material was performed. It was confirmed that during the "sparking" mode (400 V) of PEO formation, the PEO coatings, formed on PSA treated AA2024, were more wear resistant than the same PEO coatings on bare AA2024

Adhesion properties of tartaric sulfuric acid anodic films assessed by a fast and quantitative peel tape adhesion test

The adhesion capabilities of sulfuric acid and tartaric-sulfuric-acid anodic oxide films on cladded AA2024-T3 aluminium substrates have been investigated in a quantitative manner. A relatively simple, versatile and industrially applicable test methodology based on DIN EN ISO 29862 has been used. In addition, the effect of anodising process parameters on the oxide film morphology has been studied and correlated with the adhesion results. The process parameters considered are the chemistry of the acidic pickling pre-treatment step, the addition of tartaric acid to the sulfuric acid electrolyte, the formation voltage, and the electrolyte temperature. The suggested tape peel adhesion test is able to differentiate among pre-treatments and anodising conditions showing a good correlation with the morphological features at the ultimate surface. High peel adhesion strengths are measured when topographies such as pore mouth widening and dissolution-driven roughness take place. These morphologies are typically found in anodic layers formed at elevated electrolyte temperatures. The proposed method can be beneficial for a fast assessment of anodising parameters for good adhesion, which is of special interest for the industrial optimisation of anodising processes.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Team Shoshan Abraham

The Role of Anodising Parameters in the Performance of Bare and Coated Aerospace Anodic Oxide Films

The anodising process parameters (voltage, temperature, and electrolyte) control the morphology and the chemical composition of the resulting anodic oxide film by altering the balance between oxide growth and oxide dissolution reactions. The porosity of the oxide film is reduced by the addition of tartaric acid to a sulfuric acid electrolyte, while anodising at elevated temperatures enhances oxide dissolution, leading to wider pores and rougher surfaces. No significant changes in the oxide chemical composition as a function of anodising parameters was found; in particular, no tartrate incorporation took place. The resistance of uncoated anodic oxide films against aggressive media and galvanic stress as a function of anodising parameters has been studied by electrochemical methods. Anodising in a mixed tartaric and sulfuric acid electrolyte improves the resistance of the anodic oxide against galvanic stress and aggressive media in comparison to sulfuric acid ano-dising processes. However, the corrosion protection performance of the anodic oxide films in com-bination with a corrosion-inhibitor loaded organic coating is not governed by the blank oxide properties but by the adhesion-enhancing morphological features formed during anodising at elevated temperatures at the oxide/coating interface.Team Shoshan Abraham