Influence of Concentration and pH of Hexafluorozirconic Acid on Corrosion Resistance of Anodized AA7075-T6

Pinheiro, Jéssica Salles; Regio, Gabriel; Cardoso, Henrique Ribeiro Piaggio; Oliveira, Cláudia Trindade; Ferreira, Jane Zoppas

doi:10.1590/1980-5373-mr-2019-0048

Cited by 8 publications

(10 citation statements)

References 27 publications

(55 reference statements)

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“…More precipitates with slightly larger sizes were visible on the entire surface treated with H 2 ZrF 6 (Figure 2b), which is consistent with the precipitation of Zr oxide on and around the cathodic particles that were not anodized and remained on the surface, according to the chemical analyses (Table 2) and with the literature for non-anodized [8,32] and for anodized aluminum alloy [21,37]. Therefore, one can consider that the phenomenon observed after the treatment with H 2 ZrF 6 of AA7075 on non-anodized alloys occurred in an analogue way for the anodized alloy.…”

Section: Post-treated Anodized Samplessupporting

confidence: 85%

“…A certain amount of remanescent sulfur was also verified, incorporated from the anodizing bath, which was also expected and already described in literature [12,15,17]. It was possible to detect the presence of Zr on the samples treated with H 2 ZrF 6 as is was already described in previous works [21,37].…”

Section: Post-treated Anodized Samplessupporting

confidence: 82%

“…Previous studies have demonstrated the efficacy in terms of corrosion resistance of these treatments for anodized AA7075 alloy [21,37]. That improvement of corrosion resistance was attributed to a sealing behavior of the conversion coating when applied to the anodic layer, verified by Electrochemical Impedance Spectroscopy (EIS) measures, and compared to hydrothermal sealing.…”

Section: Post-treated Anodized Samplesmentioning

confidence: 92%

“…There were studies of processes carried out at 50 °C [16], 70 °C [17], or both complex and high temperature processes, i.e., sol-gel coatings [18][19][20]. However, there were some promising methods, where it was possible to improve the corrosion resistance using lower temperatures [21,22]. One of those promising recent studies has shown that a Zr-based conversion coating can be used as a protection to porous layers produced by anodizing in TSA of the AA7075-T6 alloy, at room temperature, enhancing its corrosion resistance more than hydrothermal sealing [21].…”

Section: Anodizing Processmentioning

confidence: 99%

“…That improvement of corrosion resistance was attributed to a sealing behavior of the conversion coating when applied to the anodic layer, verified by Electrochemical Impedance Spectroscopy (EIS) measures, and compared to hydrothermal sealing. A model of Electrical Equivalent Circuit (EEC) was proposed, suggesting that the nanometric ZrO 2 can penetrate into the porous layer, leading to a partial sealing of the pores [21,37]. The SEM micrographs of cross section samples (Figure 4) showed no increase of thickness when they were immersed in H 2 ZrF 6 solution, which supports the hypothesis of that nanometric Zr oxide particles could react with the outer porous layer, growing (i.e., precipitating) towards its interior.…”

Section: Post-treated Anodized Samplesmentioning

confidence: 99%

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Characterization of anodized and bare 7075-T6 aluminum alloy treated with Zr-based conversion coating

Pinheiro¹,

Oliveira²,

Regio³

et al. 2021

Tecnol. Metal. Mater. Min.

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AA7075-T6 is an aluminum alloy that has a high mechanical resistance; however, it shows corrosion vulnerability. A usual method to improve the corrosion resistance is anodization in acidic medium, which forms a thin barrier layer and a thicker porous oxide layer over the surface. This ultimate layer must be sealed to avoid electrolyte penetration. In the present work, a Zr-based conversion coating was investigated as a novel method of cold sealing and compared to the precipitation over bare AA7075-T6. The samples were characterized by Scan Electronic Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDX) to elucidate the mechanism of reaction on both natural aluminum oxide and anodic oxide layer. The hydrophobicity properties were evaluated by contact angle measurements. The mechanism of deposition suggested for the coating over the anodic oxide was analogue to the one that takes place over the bare alloy: an initial attack by fluoride ions, local pH increase and Zr oxide precipitation. It was also possible to precipitate Zr oxide inside the pores. An increase of 125% on the contact angle was observed for the Zr coating over anodized surfaces, while the increase over the bare alloy was of 32%. Therefore, a robust coating system can be proposed involving the anodic layer and the nanometric Zr oxide.

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Section: Post-treated Anodized Samplessupporting

confidence: 85%