Abstract
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.
Highlights
Aluminum alloy AA2024 is widely used, in the aerospace industry due to its superior mechanical properties [1,2]
The main solutions currently implemented in the aeronautical industry include the formation of high barrier layers together with active protection components based on corrosion inhibitors present in different parts of the protective system
The results clearly demonstrated that higher barrier properties of the outer and inner layers were observed for the systems pre-treated with phosphoric sulfuric acid (PSA) when the plasma electrolytic oxidation (PEO) coating was applied at 350 V and 400
Summary
Aluminum alloy AA2024 is widely used, in the aerospace industry due to its superior mechanical properties [1,2]. The corrosion susceptibility of this alloy is high because of the microgalvanic coupling between the alloy matrix and the present intermetallics, especially those containing Cu. The main solutions currently implemented in the aeronautical industry include the formation of high barrier layers together with active protection components based on corrosion inhibitors present in different parts of the protective system. Materials 2018, 11, 2428 layers, and corrosion protection primers were based on Cr(VI) technologies. Many countries have banned the use of protective systems containing toxic chromates [3]. A lot of research has focused on the formation of corrosion protection systems that fit with the environmental regulations [4,5]
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