The corrosion performance of self-ordered porous anodic aluminum oxide (AAO) has been studied and correlated to its structure. High purity aluminum alloy (>99.999%) has been anodized using three different conditions: (a) in tartaric-sulfuric electrolyte employing common disordered conditions (TSA), (b) in sulfuric acid applying self-ordering conditions (SA), and (c) in tartaric-sulfuric electrolyte applying self-ordering conditions (TSA-SA). Some samples were post-treated in boiling water with the aim of sealing their pores. The morphology and order of the AAOs were determined by means of scanning electron microscopy and Fast Fourier Transform (FFT), while their corrosion behavior was assessed in 0.59 M NaCl employing potentiodynamic polarization tests (LP) and electrochemical impedance spectroscopy (EIS). The evolution of impedance of samples SA and TSA was monitored during 1000 h of immersion in 0.59 M NaCl. The three types of samples present similar pore diameter (Dpo) and certain degree of order, although TSA shows the lowest. However, TSA shows smaller interpore distance (Dint), thinner cell wall thickness (tw) and higher pore density (ρpo) and porosity (P) than SA and TSA-SA, which feature very similar values for these structural parameters. The LP curves do not allow to discriminate between samples. SA and TSA-SA have higher impedance than TSA among samples not sealed, probably because a thicker barrier layer forms in samples with self-ordering regime. When sealed, TSA samples show higher impedance than SA and TSA-SA in the medium frequency range because porous membranes with lower order are more easily sealed. All types of AAO, both unsealed and sealed, undergo self-sealing process during the immersion experiments. According to EIS interpretation, TSA porous oxide is self-sealed in a more efficient manner than SA and TSA-SA. These findings imply that self-ordering conditions can enhance the corrosion resistance of AAO.

Assessment of the corrosion resistance of self-ordered anodic aluminum oxide (AAO) obtained in tartaric-sulfuric acid (TSA)

The present study focusses on laser surface modification of the plasma electrolytic oxidation (PEO) coatings developed on aluminized steel. The effect of varying laser fluency on the surface morphology and the corrosion behaviour of the PEO coatings was studied. Three different laser fluencies of 38.16, 53.42 and 68.69 J/cm2, corresponding to the 25%, 35% and 45% of the maximum power (60 W) were employed for the surface alteration. Laser treatment of the PEO coatings at lower and intermediate fluencies resulted in the development of a hydrophobic surface, thereby improving the corrosion resistance, whereas the laser treatment at higher fluency has resulted in the hydrophilic surface, with reduced corrosion resistance. The PEO sample laser-treated with intermediate fluency has produced a superhydrophobic surface with a contact angle of 153.2°. Potentiodynamic polarization (PDP) studies revealed that the PEO coated aluminized steel sample, laser-treated with intermediate fluency, exhibited superior corrosion resistance with a corrosion current density (icorr) of 1.21E−6 mA/cm2, which is 104 times lower than the aluminized steel.

Effect of laser treatment on morphology and corrosion behaviour of the plasma electrolytic oxidation coatings developed on aluminized steel

In this study, AA1050 aluminum alloy samples were anodized in sulfuric acid baths containing different amounts of environmentally friendly bio-additive (eggshell particles). The morphological, chemical, and structural characteristics of the resulting films were investigated using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction techniques, respectively. Wear and corrosion resistance of the coatings were evaluated by pin-on-disk and potentiodynamic polarization tests, respectively. The results showed that amorphous films containing less amount of sulfur would be deposited as the concentration of eggshell particles in bath increases. Moreover, coatings with more surface roughness values containing fewer microcracks would be produced in baths containing more eggshell particles. In addition, thicker films with more corrosion and wear resistance values were produced in baths including higher concentrations of eggshell particles. Those samples that were anodized in baths containing eggshell particles exhibited more corrosion and wear resistance in comparison to conventionally anodized ones.

Characterization of Anodic Films Produced on Anodized AA1050 Aluminum Alloy: Effect of Bio-additive

Compared with pure aluminum and wrought aluminum alloys, Al foundry alloys are more difficult to be anodized. The high content of alloying elements prevents the uniform growth of the Al oxide layer and enhances the embedding of defects in the anodic film. The microstructure of the substrate and the anodizing parameters play a key role in the final quality of the oxide layer. Variations in the chemical composition, casting process, and pre‐ and post‐anodizing treatments can significantly affect the anodizing response. This work aims to critically review the main factors influencing the growth and morphology of the anodic layer in Al–Si foundry alloys. In particular, the effects on the oxide thickness, surface mechanical properties, and corrosion resistance are discussed in detail.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/adem.202101480

Anodizing Al–Si Foundry Alloys: A Critical Review

The corrosion behavior of the sulphuric-anodized AA2099 using two different current densities, 0.19 or 1.0 A·cm−2, with two different sealing treatments in H2O and 6 wt.% Na2Cr2O7 at 95 °C was studied in 3.5 wt.% NaCl and 10 vol.% H2SO4 solutions. The AA2099 is widely used in aeronautical applications, thus it is essential to present good corrosion performance in chloride and acid rain environments. The surface morphology of the anodized film was characterized by scanning electron microscopy (SEM), the electrochemical corrosion behavior was studied using electrochemical impedance (EIS), and finally characterization of the surface chemical composition was revealed by X-ray photoelectron spectroscopy (XPS). It was found the 6 wt.% Na2Cr2O7 sealing treatment imparts a more homogeneous and compact passive layer, and tends to increase the charge transfer resistance, thus improving the corrosion behavior of the anodized AA2099.

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Efecto del tratamiento de sellado en el comportamiento frente a corrosión de la aleación anodizada de aluminio-litio AA2099

Studies on the corrosion performance of an effective and novel sealing anodic oxide coating

Synthesis and Microwave Absorption Properties of Sandwich microstructure Ce2Fe17N3-δ/Expanded Graphite composites

Excellent Electromagnetic-Wave Absorbing Performances and Great Harsh-Environment Resistance of Feconicrxmn High Entropy Alloys

The development of microwave absorption materials with good environmental adaptability is a hot topic in the electromagnetic protection field. In this research, Expanded graphite (EG)/ZIF-67 nanocubes-derived ([email protected]) composites were successfully fabricated by electrostatic assembly and subsequent heat treatment. The results show that the involvement of an appropriate content of [email protected] not only overcomes the problem of single EG impedance mismatch but also introduces additional magnetic loss for the absorber. At the thicknesses of 1.6 mm and 1.5 mm, an effective absorption bandwidth (EAB) of 4.52 GHz and a minimum reflection loss (RLmin) of -48.4 dB were achieved for the Z2-700 sample with a low filling ratio (20 wt%). The enhancement of EMW-absorption performance is attributed to the optimization of impedance matching and the synergistic action between multiple loss mechanisms. Electrochemical corrosion test showed that graphite nanoflakes of EG enhanced the transfer resistance during corrosion, and the corrosion resistance of pure [email protected] was enhanced with the protection of EG. This work provides a reasonable attempt to design and fabricate efficient microwave absorption materials suitable for harsh environments. 

Shiqi Zhu

Papers

Studies on the corrosion performance of an effective and novel sealing anodic oxide coating

Synthesis and Microwave Absorption Properties of Sandwich microstructure Ce2Fe17N3-δ/Expanded Graphite composites

Excellent Electromagnetic-Wave Absorbing Performances and Great Harsh-Environment Resistance of Feconicrxmn High Entropy Alloys

Expanded graphite/Co@C composites with dual functions of corrosion resistance and microwave absorption

Origin of high-frequency magnetic loss of Y3Fe5O12 single crystal thin films prepared with high-throughput screening by magnetron sputtering