Formation mechanism of Mg-Al layered double hydroxide-containing magnesium hydroxide films prepared on Ca-added flame-resistant magnesium alloy by steam coating

Nakamura, Kae; Tsunakawa, Mika; Shimada, Yuta; Serizawa, Akimi; Ishizaki, Takahiro

doi:10.1016/j.surfcoat.2017.08.060

Cited by 34 publications

(23 citation statements)

References 30 publications

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“…A number of different approaches has been used in order to obtain LDH layers directly on magnesium alloys. For example, Nakamura and Kamiyama have used LDH-based coatings for corrosion protection of magnesium alloy (AZCa612 and AZ31 respectively) 25 , 26 . In both works, the formation of LDH film was achieved by steam-coating treatment, and improvement in corrosion behaviour was demonstrated.…”

Section: Introductionmentioning

confidence: 99%

Chelating agent-assisted in situ LDH growth on the surface of magnesium alloy

Shulha

Serdechnova

Lamaka

et al. 2018

Sci Rep

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In situ formation of layered double hydroxides (LDH) on metallic surfaces has recently been considered a promising approach for protective conversion surface treatments for Al and Mg alloys. In the case of Mg-based substrates, the formation of LDH on the metal surface is normally performed in autoclave at high temperature (between 130 and 170 °C) and elevated pressure conditions. This hampers the industrial application of MgAl LDH to magnesium substrates. In this paper, the growth of MgAl LDH conversion coating directly on magnesium alloy AZ91 at ambient conditions (25 °C) or elevated temperatures is reported in carbonate free electrolyte for the first time. The direct LDH synthesis on Mg alloys is enabled by the presence of organic chelating agents (NTA and EDTA), which control the amount of free and/or hydroxyl bound Mg2+ and Al3+ in the solution. The application of the chelating agents help overcoming the typical technological limitations of direct LDH synthesis on Mg alloys. The selection of chelators and the optimization of the LDH treatment process are supported by the analysis of the thermodynamic chemical equilibria.

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Section: Introductionmentioning

confidence: 99%

Chelating agent-assisted in situ LDH growth on the surface of magnesium alloy

Shulha

Serdechnova

Lamaka

et al. 2018

Sci Rep

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“…In the case of AZ31 magnesium alloy, the film which forms on the substrate as a result of the steam coating consists of Mg(OH) 2 and Mg-Al LDH [20,21]. In contrast, in AZX612 magnesium alloy, AlOOH is simultaneously formed with the Mg(OH) 2 and Mg-Al LDH, due to the different compositions of solute elements in the alloy [23]. Thus, it would be a challenge to apply steam coating technology to the creation of a corrosion-resistant film on an Al alloy.…”

Section: Introductionmentioning

confidence: 99%

Formation of Anticorrosive Film for Suppressing Pitting Corrosion on Al-Mg-Si Alloy by Steam Coating

et al. 2018

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Al alloys offer excellent physical and mechanical properties, such as a low density, high specific strength, and good ductility. However, their low corrosion resistance has restricted their application in corrosive environments. There is a need, therefore, for a novel coating technology that is capable of improving the corrosion resistance of Al alloys. In the present study, we examined a steam-based method of forming a corrosion-resistant film on Al alloys. Al-Mg-Si alloy was used as the substrate. The cleaned substrates were set in an autoclave with ultrapure water as the steam source and processed using different temperatures and holding times, resulting in the formation of anticorrosive films on the alloy. FE-SEM images of the film surfaces showed that plate-like nanocrystals were densely formed over the entire surface. XRD patterns indicated that the film was composed mainly of AlOOH crystals. The potentiodynamic polarization curves revealed that the corrosion current density of the film-coated substrates significantly decreased, and that the pitting corrosion was completely suppressed, indicating that the corrosion resistance of the Al-Mg-Si alloy was improved by the film formed by means of steam coating.

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“…Thus, the positively charged layered structures could intercalate negatively charged substances, i.e., anions, between the layers to compensate the electric balance, resulting in the formation of Mg-Al LDH. The AlOOH in the films could be formed via a chemical reaction of the residual Al atoms and water vapor as the following reaction (Equation (3)) [35]:2Al + 4H 2 O → 2AlOOH + 3H 2 …”

Section: Resultsmentioning

confidence: 99%

Effect of Al Content in the Mg-Based Alloys on the Composition and Corrosion Resistance of Composite Hydroxide Films Formed by Steam Coating

et al. 2019

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Mg alloys are expected to be used in fields of the transportation industry because of their lightweight property, however, they show low corrosion resistance. To improve the corrosion resistance, preparation of the protective film on Mg alloys is essential. In this study, composite hydroxide films were prepared on three types of Mg alloys with different aluminum contents—that is, AZ31, AZ61, and AZ91D—by steam coating to investigate the relationship between the Mg-Al layered double hydroxide (LDH) content in the film and the Al content in the Mg alloys. Scanning electron microscopy (SEM) observation demonstrated that films were formed densely on all Mg alloy surfaces. X-ray diffraction (XRD) analyses revealed that all films prepared on AZ61 and AZ91D were composed of Mg(OH)2, AlOOH, and Mg-Al LDH, while the film containing Mg(OH)2 and Mg-Al LDH were formed only on AZ31. The Mg-Al LDH content in the film prepared on AZ61 was relatively higher than those prepared on AZ31 and AZ91D. The content of AlOOH in the film increased with an increase in the Al content in the Mg alloys. The film thickness changed depending on the treatment time and type of Mg alloy. Polarization curve measurements in 5 mass% NaCl solution demonstrated that the film prepared on the AZ61 showed complete passive behavior within the potential range of −1.0 to −0.64 V. In addition, immersion tests in 5 mass% NaCl aqueous solution for 480 h demonstrated that the film on the AZ61 had superior durability against 5 mass% NaCl aqueous solution. These results indicated that the film on the AZ61 had the most superior corrosion resistance among all samples. The results obtained in this study suggest that the LDH content in the film could be related to the corrosion resistance of the film.

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Formation mechanism of Mg-Al layered double hydroxide-containing magnesium hydroxide films prepared on Ca-added flame-resistant magnesium alloy by steam coating

Cited by 34 publications

References 30 publications

Chelating agent-assisted in situ LDH growth on the surface of magnesium alloy

Chelating agent-assisted in situ LDH growth on the surface of magnesium alloy

Formation of Anticorrosive Film for Suppressing Pitting Corrosion on Al-Mg-Si Alloy by Steam Coating

Effect of Al Content in the Mg-Based Alloys on the Composition and Corrosion Resistance of Composite Hydroxide Films Formed by Steam Coating

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