Abstract
Coatings, with a thickness of up to 75 µm, were formed by plasma electrolytic oxidation (PEO) under the alternating current electrical mode in a silicate-alkaline electrolyte on aluminum composites without additives and alloyed with copper (1–4.5%). The coatings’ structure was analyzed by scanning electron microscopy, X-ray microanalysis, X-ray photoelectron spectroscopy, nuclear backscattering spectrometry, and XRD analysis. The coatings formed for 60 min were characterized by excessive aluminum content and the presence of low-temperature modifications of alumina γ-Al2O3 and η-Al2O3. The coatings formed for 180 min additionally contained high-temperature corundum α-Al2O3, and aluminum inclusions were absent. The electrochemical behavior of coated composites and uncoated ones in 3% NaCl was studied. Alloyage of aluminum composites with copper increased the corrosion current density. Plasma electrolytic oxidation reduced it several times.
Highlights
Powder aluminum composites are promising construction materials due to their low weight, low costs, and high specific strength [1,2,3]
The thickness of plasma electrolytic oxidation (PEO) coatings formed in result of 60 min of PEO treatment on Al composite was 40 μm
The PEO process voltage-time response shows (Figure 1) that the anode voltage for the Al + 1% Cu composite was slightly higher than the voltage for the pure Al composite, which resulted in a 5 μm thicker coating (~45 μm)
Summary
Powder aluminum composites are promising construction materials due to their low weight, low costs, and high specific strength [1,2,3]. With increasing copper concentration, the corrosion resistance decreases, which is shown in a number of works [7,8,9] for the alloys: Powder alloy Al + 1–2% Cu, age-hardenable alloys 2011-T3, AA2024-T4, AA7075-T651, AA7475-T761, and experimental alloy Al + 5% Cu. with increasing copper concentration, the corrosion resistance decreases, which is shown in a number of works [7,8,9] for the alloys: Powder alloy Al + 1–2% Cu, age-hardenable alloys 2011-T3, AA2024-T4, AA7075-T651, AA7475-T761, and experimental alloy Al + 5% Cu This is mainly because the CuAl2 intermetallic compound formed during heat treatment promotes corrosion, playing the role of a cathode inclusion in these processes. In this connection, it is important to develop methods for corrosion protection of aluminum based composites alloyed with copper.
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