Effect of Cu Addition on the Corrosion and Antifouling Properties of PEO Coated Zinc-Aluminized Steel

Abstract

In the present work, Plasma Electrolytic Oxidation (PEO) coatings were produced on zinc-aluminized carbon steels (Galvalume commercial treatment). In addition, copper particles of various sizes were introduced into the coating in order to produce samples with antifouling properties. The particles were successfully embedded into the coating. A higher number of embedded particles was observed when these are in sub-micrometric size and obtained in pulsed current. The presence of particles produces significant antifouling properties on the sample's surfaces during the first 20 days of immersion. The presence of the particles reduces the corrosion resistance in comparison to the samples PEO coated without the particles; however, the corrosion resistance remain higher than the one of the untreated sample.

Keywords: Galvalume; Plasma Electrolytic Oxidation; anti-corrosion coatings; antifouling.

Figure 1

SEM image of the “large” copper particles (A) and of the “small” copper particles (B).

Figure 2

Stereo microscope images of the surfaces of PEO coatings obtained working at 0.5 A/cm² in DC mode without particles (A), with large particles (B) and with small particles (C) and working at 1 A/cm² in UPC without particles (D), with large particles (E) and with small particles (F).

Figure 3

SEM images of the surfaces of PEO coatings obtained working at 0.5 A/cm² in DC mode without particles (A), with large particles (B) and with small particles (C), and working at 1 A/cm² in UPC without particles (D), with large particles (E) and with small particles (F).

Figure 4

SEM images of the cross section of PEO coatings obtained working at 0.5 A/cm² in DC mode without particles (A), with large particles (B) and with small particles (C), and working at 1 A/cm² in UPC without particles (D), with large particles (E) and with small particles (F).

Figure 5

EDS elemental maps of the samples obtained working at 1 A/cm² in UPC with large particles (A) and with small particles (B).

Figure 6

EDS elemental line analysis of the sample obtained working at 1 A/cm² in UPC with small particles.

Figure 7

X-ray diffraction patterns of the samples obtained working at 0.5 A/cm² in DC mode without particles (A) and with large particles (B) and working at 1 A/cm² in UPC without particles (C), with large particles (D) and with small particles (E). Sample obtained at 0.5 A/cm² in DC with small particles not reported due to failure of the coating.

Figure 8

Results of potentiodynamic polarization tests (PDP) performed on the samples produced without particles and with “large” particles (A) and of the samples produced with “small” and “large” particles (B). Test electrolyte: 0.1 M Na₂SO₄ and 0.05 M NaCl.

Figure 9

Results of the EIS tests in term of Nyquist plot. In the high left, the zone at the high frequencies can be observed in more detail. Test electrolyte: 0.1 M Na₂SO₄ and 0.05 M NaCl.

Figure 10

Equivalent circuit employed to fit the experimental data coming from EIS test.

Figure 11

Visual observation (on the upper part) and stereo-microscope observation (on the bottom part) of the untreated samples after 0, 10, 20, 30 and 40 days of immersion in circulating seawater at the Hydrobiological Station Umberto D’Ancona.

Figure 12

Visual observation (on the upper part) and stereo-microscope observation (on the bottom part) of the PEO treated samples (1A UP No part) samples after 0, 10, 20, 30 and 40 days of immersion in circulating seawater at the Umberto D’Ancona Hydrobiological Station.

Figure 13

Visual observation (on the upper part) and stereo-microscope observation (on the bottom part) of the PEO treated samples with copper particles (1A UP small part) samples after 0, 10, 20, 30 and 40 days of immersion in circulating seawater at the Umberto D’Ancona hydrobiological station.

Figure 14

Scanning electron micrographs showing some diatoms found in the samples. (A) Amphora sp., bar = 10 µm; (B) Navicula sp., bar = 10 µm; (C) Navicula sp., bar = 5 µm; (D) Licmophora sp., bar = 5 µm.