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Open AccessArticle

In Situ Scanning Electron Microscopy Observation of Crack Initiation and Propagation in Hydroxide Films Formed by Steam Coating on Aluminum-Alloy Sheets

1
Department of Materials Process Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
2
Department of Materials Science and Engineering, Shibaura Institute of Technology, Toyosu, Koto-ku, Tokyo 135-8548, Japan
*
Author to whom correspondence should be addressed.
Materials 2020, 13(5), 1238; https://doi.org/10.3390/ma13051238
Received: 12 February 2020 / Revised: 2 March 2020 / Accepted: 6 March 2020 / Published: 9 March 2020
(This article belongs to the Special Issue Corrosion and Corrosion Protection for Light Metals/Alloys)
Hydroxide film was formed on 6061 Al-alloy (Al-1.00Mg-0.62Si(wt.%)) sheets by steam coating with the temperature of 220 °C for 24 h. During bending test of the coated specimens, the crack initiation and propagation processes in the hydroxide film were investigated using in situ SEM observations. The hydroxide film formed exhibited a dual-layer structure composed of an inner amorphous layer and an outer polycrystalline γ-AlO(OH)-phase layer. On the compressively strained surface, lateral cracks are preferentially initiated inside the inner amorphous layer, and propagate either inside this layer or on its interface with the outer γ-AlO(OH) layer. Digital image correlation analyses of the in situ observed SEM images suggested that the concentrated tensile strain along the surface normal localized at some parts of the amorphous layer could contribute to the crack initiation. On the tensile-strained surface, a number of cracks were initiated inside the inner amorphous layer along the surface normal and propagate into the outer γ-AlO(OH) layer. No cracks were found along the interface of the amorphous layer with the Al-alloy substrate. As a result, the anticorrosion hydroxide film adhered on the Al sheet after bending deformation. Such strong adhesion contributes to the excellent corrosion resistance of the Al-alloy parts provided by the steam coating. View Full-Text
Keywords: steam coating; aluminum alloy; hydroxide film; adhesion; microstructure; in situ observation; bending test steam coating; aluminum alloy; hydroxide film; adhesion; microstructure; in situ observation; bending test
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MDPI and ACS Style

Li, H.; Takata, N.; Kobashi, M.; Serizawa, A. In Situ Scanning Electron Microscopy Observation of Crack Initiation and Propagation in Hydroxide Films Formed by Steam Coating on Aluminum-Alloy Sheets. Materials 2020, 13, 1238.

AMA Style

Li H, Takata N, Kobashi M, Serizawa A. In Situ Scanning Electron Microscopy Observation of Crack Initiation and Propagation in Hydroxide Films Formed by Steam Coating on Aluminum-Alloy Sheets. Materials. 2020; 13(5):1238.

Chicago/Turabian Style

Li, Hongmei; Takata, Naoki; Kobashi, Makoto; Serizawa, Ai. 2020. "In Situ Scanning Electron Microscopy Observation of Crack Initiation and Propagation in Hydroxide Films Formed by Steam Coating on Aluminum-Alloy Sheets" Materials 13, no. 5: 1238.

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